There are few scenarios in which your current system may be damaged:
When you write the image to your disk instead of to a USB drive. Some tools may not let you choose a fixed disk, but in general overwriting your OS this way is possible. Mistakes happen.
When you play with the other OS, you cast commands and/or click mindlessly and you don't know what you'...
You can use dism in cmd/powershell to mount the installation iso file (more info in this official microsoft post). Then, you can disable some features through dism, or you can manually delete the files in the mounted folder and then proceed to save the image. Lots of things can go wrong if you decide to delete folders and files yourself.
A program that I use ...
External USB enclosures tend to just spin up HDs as soon as the power is switched on. It saves them having to properly negotiate with an unknown controller & OS as to when to spin up/down.
The end result is that there's always sufficient activity to keep the casing slightly warm.
SSDs will suffer from this less, as there's no mechanical component, but ...
USB is backwards compatible. The communication across the port will only occur at USB2 speeds, but that will not be a significant issue for installation.
I've installed Windows 10 many times from USB2 drives over USB3 ports, and never had any issues. There's been no need to install drivers or anything.
Windows 7 is a very old OS compared to Windows 10. I ...
It is an old thread, but I didn't see anybody mentioned Ventoy.
You can create bootable usb with it, and then just copy and paste the ISO/IMG files.
Ventoy is an open source tool to create bootable USB drive for
ISO/WIM/IMG/VHD(x)/EFI files. With ventoy, you don't need to format
the disk over and over, you just need to copy the
ISO/WIM/IMG/VHD(x)/EFI files ...