How to pass a command that may contain special characters (such as % or !) inside a variable to a for /f loop?

Question

I have a few nested loops in my code and in some point, they're divided by a call to a label like this:

@echo off
chcp 65001
for /r %%a in (*.mkv *.mp4 *.avi *.mov) do (
    echo Processing "%%~a"
    call :innerloop "%%a" "%%~fa"
)
:: Instead of goto :eof, I chose cmd /k because I want the command prompt to still be open after the script is done, not sure if this is correct though
cmd /k

:innerloop
setlocal EnableExtensions EnableDelayedExpansion
for /f "delims=" %%l in ('mkvmerge.exe -i "%~1"') do (
:: Probably this would be a safer place for setlocal, but I believe that would mean that I wouldn't get to keep a single, different !propeditcmd! per processed file
    echo Processing line "%%~l"
    for /f "tokens=1,4 delims=: " %%t in ("%%l") do (
:: This section checks for mkv attachments. There are similar checks for chapters and global tags, all of those are handled by mkvpropedit.exe
        if /i "%%t" == "Attachment" (
            if not defined attachments (
                set /a "attachments=1"
            ) else (
                set /a "attachments+=1"
            )
            if not defined propeditcmd (
                set "propeditcmd= --delete-attachment !attachments!"
            ) else (
                set "propeditcmd=!propeditcmd! --delete-attachment !attachments!"
            )
        )
    )
)
:: Since !propeditcmd! (which contains the parameters to be used with the executable) is called after all lines are processed, I figured setlocal must be before the first loop in this label
if defined propeditcmd (
    mkvpropedit.exe "%~f1" !propeditcmd!
)
endlocal
goto :eof

The script works for most files and is divided like that to allow breaking the inner loop without breaking the outer when a pass is reached. While it works for most files, I noticed it can't handle filenames containing parenthesis % in their names, likely due to EnableDelayedExtensions.

Normally, I know I would have to escape these characters with a caret (^), but I don't know how I can do it if the special characters are inside a variable (%~1).

Is there a way to do it?

Update: I've been working a way to separate the section that needs delayed expansion from the one that needs it off just find in the end of my code the line mkvpropedit.exe "%~f1" !propeditcmd!, which both needs it off and on due to "%~f1" and !propeditcmd! respectively. I think this means there's no way around the question and escaping will be necessary.

Continuing my research, this answer seem to suggest this could be achieved with something like set filename="%~1:!=^^!". Nevertheless, this doesn't seem to be the proper syntax according to SS64. I'm also unsure if this will replace all occurrences of ! with ^! and I'm also concerned this kind of substitution could create an infinite loop and if wouldn't it be more adequate to perform this by first replacing ! with, say, ¬ before replacing it ^!.

While I intend to do testing soon to determine all of this, I'm worried I may not cover it all, so more input would definitely be appreciated.

---

PS: full code (88 lines) is available here if more context is needed, although I'll edit the snippet in this question as it may be requested!

Edit: I didn't think it was relevant at first, but now I think it helps to know what is an standard output from mkvmerge.exe -i:

File 'test.mkv': container: Matroska
Track ID 0: video (AVC/H.264/MPEG-4p10)
Track ID 1: audio (Opus)
Track ID 2: subtitles (SubRip/SRT)
Attachment ID 1: type 'image/jpeg', size 30184 bytes, file name 'test.jpg'
Attachment ID 2: type 'image/jpeg', size 30184 bytes, file name 'test2.jpg'
Attachment ID 3: type 'image/jpeg', size 30184 bytes, file name 'test3.jpg'
Chapters: 5 entries
Global tags: 3 entries