You will be hard pressed to see salamanders out on a 26+ C day. Most Ambystoma will not appreciate temps above 25 C for long periods of time. Sure salamanders can endure higher temps for a couple of days but it will potentially be life threatening. Stress is the name of the game and at higher temps the immune system drops causing a swift take over.
As stated above many aquatic newts can thrive in higher temps but I do not know one that will survive temps above 28 C for more than several days. Cynops cyanurus (most Cynops in fact, but cyanurus is the best) and Neurergus strauchii seem to do fine in lower 80's but if it spikes higher than it can be a problem. There are more but these two species I know live in areas were the temps are warmer and will do good in this range.
There are also cheap effective ways to keep your tank cooler if needed. Also as stated earlier bottled ice, open top (screened), well ventilated, coolest part of the house/room, etc. This will go a long way to keeping temps down. Here in Wisconsin during the summer if I didnt keep my collection down in the basement, I would run into major problems myself.
I would definitely not bet on or expect an adaptation to the higher temps. Just like fish, if you do not keep them at the right temperature range its only a matter of time. You would not subject tropical fish to 10 to 15 degrees lower than their natural temp range would you?
I agree with them being wonderful creatures and I wish you all the best!
Mitch