This thread seems like a pretty slippery slope here but I will just chime in with my 2 cents.
Honestly in my opinion, recasting any item (even with slight modifications) that was designed and is being sold by someone else - regardless of that format - should not be an acceptable practice. Changing one small portion of a prop and selling it as your own is just crazy to me. For example the previously mentioned WastedFett deathwatch helmet being a recast of a Boba Fett bust with the dent filled in (if that is truly the case as it is the first I have heard of it) should be a no go as the original item was bought as an already licensed product which is also being produced.
If someone were to take the dimensions of the already existing helmet and carve it entirely out of clay first, design it on some sort of 3D software, or scratch build it from the ground up and then mold and cast that - totally acceptable. However, altering 1 small thing and claiming it as your own would be like copying the entire Harry Potter series and only change the main characters name - someone else did the majority of the work that you are claiming is yours but because you the main character's name was changed it is now yours to make money off of? I can't get behind that.
Or for another example, I sell casts of a vibro dagger that I personally designed and created the master of. The vibro dagger has an opening in the blade - if someone were to fill that opening, cast it, and then started selling it as their own, you bet I would be causing a ruckus for sure. However, these large companies that produce some of this stuff probably aren't on these forums, so there would be no way to know someone re-casted their product or altered slightly and re-casted and is selling it. That would 100% be a winnable lawsuit by the company if they could prove an actual recast of their product - regardless of a slight modification.
Obviously there are some exceptions to that rule, as it is my understanding that some of the helmet vendors here have been given or gotten permission to use and sell casts of the original helmets from the movies or there are other "found" items that are no longer in production that other members have made casts of and sold. The first being acceptable as there was specific permission given and the second being out of production items which limited availability and also weren't initially specifically designed for the purpose of Boba Fett costuming.