I've converted a few games over time. A lot of ideas are based off cultures rather than tags, so if you have say an English-controlled kingdom of Ireland, you'll have English ideas. Norse doesn't have anything special and I believe actual Irish ideas stem from Irish culture, so you'd probably end up with Generic. The mappings would also be doubly messed up, since being Norse-cultured Ireland will be renamed to its localized form, "Irland".
Regardless if you have some patience, you can modify the converted files and just give yourself any ideas you want. It's actually not terribly hard to do, but it can be tedious since you have flip through many files until you stumble upon your nation. If you want a guide, I learned to mod in my own ideas by using this off of Reddit:
https://www.reddit.com/r/paradoxpla...o_you_change_national_ideas_after_converting/
On a side note, whatever you do try and keep your Council laws at "Not Empowered" if you have Conclave otherwise you'll probably end up with multiple vassals with some liberty desire. If you don't have Conclave, then shoot for higher levels of crown authority to ensure you have no vassals to deal with. Also, when you go onto to converting try and do it when there's not a ton of rebellions going on because they tend to stall the converter.
