I have a 4506 from which I need to remove the right side safety lever. I’ve seen a video showing how to insert a pin into the small hole on the lever to depress the Safety Lever Plunger, but when I try that the lever will not slide off even with the plunger depressed. Is it necessary to remove or advance the firing pin to allow the plunger to fully depress?

No other actions are required, pushing the plunger down should release the lever. The lever may be held by some seized lubricant or oxidation. Try applying a bit of penetrant to loosen the lever, and perhaps tapping the end of the lever with a "non-marring" plastic tool or punch after depressing the plunger.
Use caution. The plunger is under considerable pressure....cover the cavity in the manual safety body with your thumb while sliding the lever off.

__________________
Ret. LE, FA Instr, S&W Armorer

Great, thank you for the help. :-)