How does the physical size of resistors effect replacement of them?
For DC and even up to high-frequency AC, the issues are typically only mechanical, not electrical.

However, for very high-frequency AC (VHF or UHF radio frequencies), there may be other factors to consider like bulk capacitance and lead inductance, etc. 

So this question/answer doesn't hold up across the entire spectrum. Since we don't know the nature of the circuit, be aware that this is not a 100% universal answer.