My personal experience with ammonia is that it will DEFINITELY REMOVE PAINT , so I would not use it near your frame paint.
I've used it to carefully remove overpaint from bicycle frames (rinsing wit h soapy water and/or vinegar immediately), plus to strip paint from ant ique wood furniture. Recall a friend of mine who soaked some grimy antiq ue auto license plates in ammonia, only to be shocked to find all the paint dissolved off the next day (it also removed the greasy grime!!!).
So my advice is not to use ammonia anywhere near your frame paint unless it is fully protected against contact.
The archives is loaded with advice on removing frozen seatposts.
Regards,
Kevin Kruger