I’ve definitely made similar errors dual booting. I don’t know what your budget or hardware is like but if you can fit a second hard drive in your computer it is very worthwhile for distro hopping.
The second hard drive will let you install whatever boot loader the USB installer wants to install without overwriting the bootloader on the first hard drive.
Modern grub is pretty magical and should detect both OSs either way.
But yeah that’s why there are so many warnings in every Linux distro about installing grub. You do not want to mess with a currently working bootloader.
This is mostly because the bootloader needs to be in a very specific location on the hard drive and so you can’t just install it anywhere. Which means you have to overwrite the old boot loader if you choose to install a new one.