I don't think you can assume that you will be sensitive to methylfolate. But you can start with a few crumbs and work up, if that helps.
If you can't tolerate methylfolate in supplement form, you can try foods high in methylfolate. Others can help you out with what those are. The precursor closest to methylfolate is folinic acid, but if you have the MTHFR C677T mutation, your ability to convert it will be compromised. If you have the MTHFR A1298C mutation, taking folinic acid may keep you from having a healthy biopterin cycle (that makes neurotransmitters). How that affects you would depend on your other mutations, but may include depression, agitation, anxiety, sleepiness or wakefulness, or other. You'd just have to look out for them.
Sorry not to be of more help.
Crit