Just include an option in some configuration file which is initially turned on, and with a disclaimer that if it's turned off gameplay beyond end date isn't supported by Paradox.
I agree the limit is pretty annoying when you just want to play a few more years to see how something would've turned out on its own, despite techs probably being maxed etc.
I agree the limit is pretty annoying when you just want to play a few more years to see how something would've turned out on its own, despite techs probably being maxed etc.