Exactly how we did it too. We created the editor/assembler that peeked to see what was there and display it in Assembly, Hexadecimal, and ASCII.

You could edit whichever version you wanted and it would Poke it into RAM.

You could also save swaths to a file.

Back in High School in the 80’s me and a buddy wrote a Z-80 editor assembler in TRS-DOS BASIC.

It was not rocket science.

Not an expert, but I don’t think replacing the TPM chip is an option.

How did you run a memory test? Do you get a command line?

This looks like something that I would find extremely cool if I had any idea what it was.