Much as it would pain me to do it, I'd stick out for the year with your current insurer. Then, at renewal time get all your quotes with the remap and stated power gains and get it remapped then.
IIRC your first year with an insurer they will properly try and screw you over if you cancel (I have a feeling you'll get no refund for the remaining 4 months but I'm not 100%).
Also, having a blanket BHP gain is ludicrous in this day and age, a better way would surely be to do it as a percentage power increase (as all my insurers have asked previously), with 100BHP making a 44% increase in power over the stock (quoted) figure. Also, we all know that there are many cars out there regularly exceeding the quoted power - even APR measured a (I think) US spec non PP GTI at 235 BHP (from a quoted figure of 210), meaning an increase on your car (for instance) of 82BHP (or 34%)
Insurers are a funny bunch. Had a tuning box on mine and took it off, rang my insurer to let them know and my policy was reduced by... Zero.
Funnily enough though, I bet they would have put up the price if I added it though!!