vim-enmasse VS vim-scriptease

You can use the quickfix/location list and either use :cdo or use a quickfix edit plugin like vim-enmasse:

I highly recommend vim-enmasse.

My old style VimL plugins with CI https://github.com/Olical/vim-enmasse/

To add a third plugin to the list of those already mentioned in the replies (yep, I've read that you can't install plugins in your case – sorry for not directly helping you out OP!): There's also https://github.com/Olical/vim-enmasse – which hasn't been updated for a while, but which I've (literally) been using for years for exactly the described purpose.

The only other example I have is an older plugin of mine: vim-enmasse - that's traditional vimscript so it might be a better example for you.

I use tpope/vim-scriptease's :Messages instead.

Another great tool is the Scriptnames command from the vim-scriptease plugin. It dumps the output of :scriptnames into the quickfix list, letting you open all the files vim is reading to help with troubleshooting.

And the tpope extension comes in handy: https://github.com/tpope/vim-scriptease

As you continue your journey into vim plugin dev, I'd recommend vim-lookup and vim-scriptease.

This seems related to the g= mapping from vim-scriptease. I personally also have the following two mappings defined in ftplugin/vim.vim:

FYI, tpope/vim-scriptease provides this bound as an operator g=. You may want to read that implementation to see what you can learn more advanced techniques for writing vimscript. With the operator, you can g=W to convert the WORD to a solved expression.