I would suggest that keeping the same is probably about right.
Basically if you are correctly weighted without the bailout what you need to do is figure what is the situation when its use is required.
Presumably you will have lost all your back gas. Therefore you are more positivley buoyant than usual. Now you are using up the gas in the bailout and need to make a safety stop. The bailout is more buoyant than normal since it is typically full.
Taking weight off seems odd to me. However, the only way to be sure is to do a proper weight check. Either with the main tank at 10 bar and using the pony or with the pony at 10 bar and using the main tank.
I guess if the pony is 3L steel and the reg/SPG are heavy items some small weight loss is possible. But this will vary according to what you have chosen. An Ali tank will probably require adding weight.
So, in short do a weight check and don't rely on what you read here