My first foray into Seiko modding...

I want to understand the difference between modding and creating franken watches! Can someone please explain?

There is a guy modding Seiko. They look alright but isn't this modding thing like getting high quality replica cases of costly brands (in this guys case) and putting in Seiko movement dials and hands ?
Attaching some pics that I got from his handle. Would you ever buy something like this for yourself ? Won't you feel that you are wearing a fake watch ?

Thats a really slippery distinction. In my opinion, a mod starts with the OEM piece. It can be a complete watch but at the minimum, the case and bezel. If you replace the dial with a sterile one, that's fine but if it's an attempt to pass an AM as the genuine article, then you have a franken.
If you have a piece in the mod that's trying to pass off as something it's not then you have a franken.
When it comes to the movement, if you're replacing a movement with a genuine piece, then it's a mod. For example, if I replace my 7S26 with a an NHxx then that's a mod. What if I replace the mainspring, balance assembly and the escape wheel in an NHxx with those of a 6R15? In my books, that's a mod.
Long and short of it, if I replace parts with the sole purpose of cutting costs then that's a franken 95% of the time. The other 5% is when the parts availability and costs are just extortionate and I end up having to buy cheaper due to lack of fair value in the market.

Repairs, which wasn't the question asked, can also create a franken and the same rule of thumb applies. If you're cobbling together a mish mash of parts from a variety of pieces, then you can create a franken. However, if one is judiciously inspecting, checking and creating a piece that performs as good as or better that the starting pieces, then you have a mod. The fine line is the skill used and intent.

Whether I'd buy the watches myself, the answer is no. Those watches are homages at best and highly likely to be fakes (AM dials). A mod is commissioned not an off-the-shelf complete piece and in all cases the market cost of individual parts is a lot more than the final piece.

As you can tell, I've tried to describe something that's borderline art and might've failed to make a clear distinction. One man's mod might be considered a franken by the next person.