Substituting birds eye chilli with carolina reaper
Capsicum chinense chili peppers tend to have far more pronounced smoky/fruity aromas than small capsicum annuum types like bird's eye - whether this aroma works well with the rest of the dish is probably a case-by-case matter.

Recipes/cuisines that use mixed fresh green and dried or fresh red chilies in their flavor profile (eg many indian dishes, some hunan chinese dishes...) can probably gain from using that kind of pepper - recipes that only use dried red types might rely on the peppers not adding unexpected aromas.

Another rough thought experiment to categorize dishes: Would the dish gain, or be ruined, if you added sambal oelek into it (which tends to also have a somewhat smoky/fruity note to it)?

Mind that distributing the heat through the dish is an important matter with peppers that hot - so infusing the fat and cutting the peppers very finely is advised. However, these actions both have their own dangers with extremely hot peppers: Frying them in oil can suddenly surprise you with releasing a lot of capsaicin into the air, teargassing/choking you; cutting them finely usually means touching them a lot. Keep a wet towel handy, expect to have to dash outside for fresh air, and use gloves if inexperienced.

Mind that fresh red chilies seem to be uncommon in making thai curry pastes (except some recipes for kaeng pa ... which, however, due to the lack of coconut milk, could end up truly hellish with a 2+ million scoville pepper in the paste), a bit more common in indonesian-style pastes...

Quick pickling them as a condiment to a pad thai, or using them in a som tam, is probably ill-advised - that kind of heat is usually just plain unpleasant in lean preparations...