If two “DNA Surgeries” are active on the field, the one that resolved most recently takes precedence.
Netrep Q&As:
Q: If I have 1 or more Machine-Type monsters on my side of the field and I activate “Limiter Removal,” and before the end of the turn I activate “DNA Surgery” choosing something other than machines, will they still be destroyed?
A: Any monster that is doubled by “Limiter Removal” is destroyed at the end of the turn, unless it is no longer on the field. This includes if it is no longer a Machine at the end of the turn. bishop, 12/08/2003