All the best with the compo entry
Yeah, an "undo" command would be nice, but would require a modest amount of elbow-grease that I couldn't fathom right now.
But as for easier access to cut/copy/paste, I've made a commit to the repo where I've provided a few new commands to the "Edit" menu.
To retrieve my latest commit from the mercurial repo, you will need to do two commands in your TortoiseHg gui again, "pull" and "update"... Sorry for yet another painful pairing of mercurial commands
"pull" = retrieves the latest commits from the online repo into your pc's local repo
This lets you see my commit in the commit-history of the gui, but it doesn't affect your current source files, they remain as they are. Eg, if you currently have edits that you haven't committed yet, you won't lose them.
"update" = right-click on my new commit and select "update". This then updates the source on your drive to my latest commit.
There's a chance this might fail, if it notices that you have edited a file on your local-pc that it wants update with my version. It might offer you to merge or force-overwriting. If you're lucky, it might even successfully auto-merge our changes

But in the worst case scenario, if the thought of learning the "mercurial merging" process makes you want to puke, then don't try that for now. Just copy your changes to another backup folder, force "update" your main folder to my new commit, then copy over your changed files from your backup folder into your main folder.
I know... It's annoying... You're going to hate these steps just as much as "commit" and "push" from last time... Perhaps you'll hate them even more!
As for info on my commit, my added commands are:
- "Cut Block" = CTRL+Shift+X (or also the prior Shift-Del)
- "Copy Block" = CTRL+Shift+C (or also the prior Ctrl-Del)
- "Paste Block" = CTRL+Shift+V (or also the prior Shift-Ins)
Some caveats though:
- I chose these "CTRL+Shift" shortcuts due to the standard CTRL+X/C/V presently being used to draw various petscii chars
- One side-affect of "CTRL+Shift" shortcuts is that the app presently uses this key-pair to toggle between upper & lowercase charsets
- To try workaround this, I tried disabling the charset-swapping behaviour if you use the CTRL key on the right-side of your keyboard
Ie, I thought it'd be nicer to preserve the left-CTRL key's behaviour to emulate the commodore-key, as its position was also in the bottom-left. Although one downside of this choice is that most people prefer to do cut/copy/paste with the left-ctrl-key too. So doing it with the right-ctrl-key might feel a bit awkward too.
As for the shifted-characters, I haven't had a chance to ponder it through, but would something like this work? Let a particular 'unique' ibm-ascii key equate to "c64-shift-key" and another one equate to "commodore-key". Eg, '~' (tilde=shift) and '|' (pipe=commodore). So that "P (shift) R" would equate to "P~R" and the parser code could identify these special characters and "shift-ify" the character that follows it?
PS. I visited your site and saw your wiki on Channel F / VES programming. Wow, I never knew about that gaming hardware before, I had to google it to learn more

It takes a lot of enthusiasm to share a wiki like that, congrats to you
