This tailblock method works at best if you use it on forehand. So in case of a ruddertip: you implant the hardwooden tip before covering the new shaped rudder with fibres/resin.

But even later on, like in your case, you can sort of use the same method:
Make a nice clean oblong hole with your dremel in the tipside of your damaged rudder. Then you fill this with rather stiff and hardened compoundpast (so made with use of colloidal silica powder).

This can ofcourse only work if the sides of the rudder are not too much damaged.
But even then you can laminate a small peace of the side part again with a "slanting joint".

You have then also created a tailblock on the ruddertip, but not of wood, but of epoxycompound. This will certainly be more resistant to abrasion and bottom crashes.

And you can repeat this procedure again infinite.