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[Chimera]

I think you could even up their sizes through feeding but the fact of the matter is this would have to be done over time. The question is a bit open ended as you haven't mentioned what the size difference is either.

So long as both snakes are being fed an amount that will keep them healthy (i.e. your not overfeeding or underfeeding) there should not be an issue. There is no exact amount to feed a snake so you could feed the smaller one in the upper range of what is healthy and the larger one in the lower range.

Reptiles biological systems move slowly and therefore any quick results are often unhealthy.