Can disabling secure boot affect Windows?

Solution 1:

No.

Disabling/enabling SecureBoot doesn't affect already installed operating systems in any way.

The only thing SecureBoot (if enabled) does is to verify that the Operating Systems bootloader has a valid security certificate and it refuses to boot it it doesn't have one.

With SecureBoot disabled that check is simply skipped and the UEFI bios will happily load any operating system, regardless of whether or not it has a certificate.

I have personally installed at least a 100 systems (Windows and Linux) with SecureBoot off and enabled SecureBoot later without any issues.
(Had to switch it of because my installation medias are created with Rufus which uses a UEFI NTFS driver that doesn't work under Secure Boot.)

EDIT: As Akeo pointed out in the comments, a few hours after I originally posted this answer Rufus was updated and now works WITH SecureBoot enabled.