Can I do a leakdown test on a cold motor? The motor is out of the boat and I am unable to run it. Do you usually see higher numbers on a cold motor?

Yes, leakdown past the rings will be higher, valves about the same. This would still be an indicator if one or two cylinders are markedly different.

most of them are done cold anyway, no one checks a healthy motor.

A cold leak down test on an engine that has been running is fine. Percentage of leakage will be higher. If the engine has set some time it is a good idea to warm the engine up to free up an crystaliztion on valve seats and such.

What would be an acceptable amount of leakdown on a cold 502??

How many hours are on it?

About 100. I guess a better question would be how much difference would you see from a cold motor to a warm motor?