Is low IL (integrity level/label) a supported scenario?

[GeeLaw]

I'm considering developing preview handlers using Windows Forms, and I want the preview handler to be portable. This means it can be used by a standard user without requiring administrative privileges upon installation. I plan to achieve this by registering the handler under HKCU.

As of Windows 11 version 24H2 (I have no idea if this has changed since Vista), the most important host of preview handler (File Explorer and Common Dialogs, basically the shell) will only allow opt-out of low IL if DisableLowILProcessIsolation is set to 1 under HKLM, making it impossible to develop a medium-IL portable preview handler. Hence the question.

(Side note: Outlook (Desktop), the second most important host of preview handler, doesn't do low IL isolation and will happily run preview handlers at medium IL.)