Sorry for my ignorance but what tool and instructions??It's perfectly acceptable and I encourage you to add an extension if that suits your needs.
If done by making the end splices looped using the splicing instructions and tool provided with many of these ropes, you can easily replace a broken or damaged section or adjust length on the fly.
My current rope is made in sections of orange, blue, yellow and maybe a couple other colors just to make it flashy. I placed a small pool float just fore of the handle harness so the driver can easily identify the location of the handle. This handle section FWIW, is easily removable in case of tubing where you might not want or need the small pool float.
75ft length is perfect, IMO.