It should be OK if it is a volume control.
You just want to look at what is the signal going to the Pot coming from, to make sure it can drive a lower impedance like 10K. If it is from an Opamp output, it should be OK. It is is a valve amp, it may not be able to drive 10K. Same is possible if it is from a transistor collector, but if it from a transistor emitter, it will be fine.
The simplest test is if you put in the new Pot and the volume hasn't decreased, there is a very good chance that it is fine.
Also there may be a series capacitor going into the Pot that was chosen for the 100K, so a lower capacitor may be required. Anything on the Pot output will be fine as it is.
Now if you need to replace any tone control Pots, then the 100K value is important.
Richard.