It won't make any difference in theory.
MOT has nothing to do with how fast your car is. BUT... if the remap makes your engine run too richly, for example, then there is a slight slight possibility that your emissions will be out.
So, if you can turn it "off" easily then perhaps your engine will run more leanly and so less emissions. However, common thought on the subject says that a remap makes your engine more efficent. So less bad emissions. Perhaps.
I think I've covered my back enough there!
The worst for about MOT's is headlights & indicators. They WILL claim that your indicators weren't orange enough and charge you 5 quid a bulb to replace them. This is virtually standard practice at a lot of dodgy MOT places (not saying yours is dodgy
) So you could save yourself a few quid and buy some new ones. Then when they say "Ooo, your indicators aren't good enough" you can produce a receipt for the new bulbs and slap them in the face with it.
Also worth checking your tyres. If the need doing - get them done first. They might charge you for another MOT if you take it away to get tyres fitted at a more resonable rate.
I've got a fair bit of experience in getting cars through MOT's!
Cheers, Will