I do not think I have parsed this correctly; it sounds like you are averse to mixing government types within one realm, which converting to a religion incompatible with Confucian Bureaucracy would achieve? That is the case in vanilla though: nothing is stopping a feudal realm from vassalising a Chinese one, etc. And wasn't the point of ConBur that it did not care what religion its vassals have and cannot revoke them for it? Ergo, it shouldn't care if they are feudal, monastic feudal, theocratic, Japanese Imperial etc. either, right?
I don't mind the government types in a realm sometimes becoming a mix, and it will still be possible for that to happen in various other ways (e.g. you could convert to Sunni after that spreads along the Silk Road and ends up in your realm, or you could swap to a different culture), but these particular decisions were meant to only allow (the culture-appropriate subset of) conversions that didn't result in that.
As for religious revokation not being possible if you've got the Confucian Bureaucracy government (or Chinese Imperial), that is the case, but since a more open decision would have the potential for conversion to a reformed faith that isn't "Chinese enough" and that thus doesn't get Confucian Bureaucracy it would create issues from the other direction (e.g. I want to weaken certain vassals, so I flip to a version of Reformed Shenist that isn't "Chinese enough", pass religious revokation (we'll assume I've depowered the council so that it doesn't matter or that I can force it through), and go on a revokation spree (and maybe convert back later)).
While we potentially might open up Confucian Bureaucracy slightly more, we're not going to make it something that you can get with any reformation of a religion that has the potential to be "Chinese enough" since there are reformations that seem like they wouldn't be particularly likely to result in a religion that is unlikely to consider a multi-religious society to be a great idea (e.g. Dogmatic anything), and we also want the option to intentionally reform to a religion that wouldn't be "Chinese enough" (or "Viet enough", or whatever) to escape from Confucian Bureaucracy (and/or Chinese Imperial), since some people might want to do that.
Right, that's a valid gameplay argument; though if I recall correctly, the vanilla Dharmic religion decision can only be taken once a lifetime. So no temporary flipflopping possible there.
I'll grant that vanilla doesn't allow multiple conversions using the Dharmic decisions, and something similar could (and probably should) be added for these decisions (there currently isn't anything like that, since I based the script for the Chinese/Viet/Korean decisions on the script for the Jurchen one-way conversion decisions that didn't have the check as there's no decision for reconversion) but the decisions still make it easier to move between religions than it normally is (you'll still have the "Convert to secret religion and instantly go public" option, the "Move capital and convert to local religion" option, and a bunch of other less straightforward options for the conversion or conversions that you'll be doing outside of the decision), and I don't really think it needs to be easier in a more general case.
I agree that a specific "convert to the pagans we used to be" decision would be out of scope and lacking from vanilla, but that was not what I was suggesting: only for the decisions you added to be congruent with the vanilla Dharmic decision.
It of course depends on how exactly you interpret the rationale of that decision. Does it mean: "in this realm we do not care about religion, so feel free to follow any that we are accustomed to"? Then it would make sense for Koreans/Viet living in a Chinese Realm, to not be able to convert to a religion China is not comfortable with. But it would not make sense for people living in a Korean/Viet Empire of their own making, which doesn't even have to have the Confucian government type, and ergo, does not even have to be religiously tolerant. Easy solution: only allow these decisions if the top liege is a Chinese Bureaucracy.
If the rationale behind the vanilla Dharmic decision is independent of the current realm, and rather goes like "these three religions are our cultural roots, and we do not care which of them you follow so convert away!" it again makes no sense for a weird version of a character's ancestral religion to be excluded, because by definition it is part of the cultural heritage.
How do you interpret the Dharmic decision?
I interpret the Dharmic decisions as "These religions, with these historical features, would normally be okay with conversion from one to the other, and thus there's an easy way to do that", and the new decisions are meant as something similar (with "these historical features" replaced by "these features that are reasonably close to the unreformed religion, Buddhist, and Taoist" in the case of reformed pagans), restricted to a small set of cultures that can get certain government types that would work well with multi-religious realms, and with the conversion to/from the pagan religions also being restricted to the cultures that seem the most likely to swap to them (as e.g. a Korean Silla swapping to Thanist shouldn't be particularly common compared to it swapping to Muist and it thus feels like the former swap doesn't need to be allowed with a decision).
As for the potential Korean/Viet feudal realm that doesn't have Confucian Bureaucracy or Chinese Imperial, there are currently only two ways that situation could arise in Tianxia (at least as far as I can remember): You're already following a religion that isn't "Chinese enough" (e.g. Catholic, Sunni, Norse, or a weirdly reformed Muist), or (assuming you've not become a pretender empire (and thus Chinese Imperial), as that takes precedence) you hold the ERE/RE (the Roman Government takes precedence over Confucian Bureaucracy, since the PDS devs have decided that that is an option regardless of religion and culture (we've make Chinese/Japanese Imperial take precedence, in the unlikely event that either is relevant, but have otherwise not restricted it further)). In the former case, I don't feel that the conversion needs to be easier (except possibly for a future, slightly expanded "Korean/Viet enough" set of reformations that would allow Confucian Bureaucracy but not Chinese Imperial) as you've moved away from "This religion is historically compatible with Taoist/Buddhist", and in the latter case the conversions would still be an option since nothing in the decision checks if you're Roman Imperial.