If is is a Rubber Snap Plug, and you can reach it easily from the inside, go for it.
The tapered threaded brass plugs will only fit from one direction.
As long as the hole is plugged, it makes little difference.
... though (IMHO) the water pressure pushing in on the plug can help push it out of the hole if you place it inside the boat. I prefer it on the outside, myself.
If it is a normal garbor plug you will need to put it in from the back. It is a tapered tread from the back to the front. If you use a snap type it might work from inside but I would recommend a screw in type for better piece of mind. The snap in scare me.
I have used the snap type from the out side for 20+ years with no touble. I used a length of stainless wire to attach the plug to the engine mount to keep from loosing it. However, it has never come out. It is easy to see when getting the boat ready to launch. Make sure the handle doesn't project into the wake. This can cause it to rotate into the release positon.
Yessir....you definitely want a lanyard attached to that plug or you might get a bit uncomfortable holding your finger in that hole until someone comes along with another plug.
