We do that operating out of Penang.
The runway is pretty darn rough indeed there, and if you use the full reduction allowed then there would be very little runway left at Vr.
We have a company memo out stating that full thrust must always be used there - But we normnally wouldn't get a lot of reduction there anyway due to the weights we operate at.
As for lighter weight planes, at say Bombay, I don't know. If the Captain decided to use something between the appropriate reduction and full thrust and something went wrong then he's be in a spot of bother all right.
If in doubt, go for full thrust ...