I understand what you're saying. Changing the octave/instrument applies changes to the complete grid.
A way to get around this problem is to program octave 4's in one grid, save to the loop, and add another layer of octave 5's.
I could easily program supporting multiple instruments/octaves in a single grid but I'm not sure if that'll be intuitive to use. I'll do some research on this.
I just saw your comment, I couldn't reply to it there, but I just added the edit layer feature, along with other QOL features.
Also, did you try the preview with loop button? It's in the preview drop down. It should let you preview the grid along with what's already in the loop.
Yup I'm thinking of ways to make it shareable. This is a client-side static website(runs completely on your end) so won't be able to make backend-supported links.