Tricub, you rebored my TY250B about 10 years ago and used a Wiseco DT250 piston and it has been very good for durability.
A local motorcycle mechanic rebored my TY250D motor (the one in the Majesty) and also used a Wiseco DT250 piston and it has also gone very well but that was only 2 years ago.
The Yamaha DT250 piston is the same in all the important dimensions as the Yamaha TY250 piston. Yes the TY250ABCDE can all use the Wiseco DT250 piston. From memory the windows are a slightly different shape in the DT piston, and this can be fixed by reshaping them. I don't remember how close in shape and position the Wiseco rear windows are to the Yamaha TY250 piston windows, but I remember that I didn't reshape them before use.
The TY250E barrel is the same design as the C and D models
The internal design of the B model cylinder is the same as the CDE models but is quite different externally to the CDE models.
The A model cylinder is different externally to all the others, and I have never had to pull my A model head or barrel off so I don't yet know how different it is inside to the others.
As good as the Wiseco pistons have been that I have used, I would still prefer to use original Yamaha pistons because they are quieter from a cold start and have proven themselves to be incredibly long-lasting and reliable.
relax, nothing is under control