You've asked a bunch of questions and some are relatively painless to answer.
Yes, there are relatively inexpensive tools that you can buy to edit ribbons with.
Absolutely, you can edit the zip file's xml components but as you discovered, it won't work if you make a mistake with the code. Editing the zip file is easy but it is also easy to make a mistake which prevents the ribbon code from loading.

It is possible to create ribbon customisations that don't require vba code. So in that case your dotx/docx file is already safe and therefore trusted. However most customised ribbons do make use of code and the authoring of vba code is easier than the authoring of ribbons. Assuming your customisation requires code then (as recommended by Italophile) you would sign the code in the file and install the public key certificate on your user's machines so they can see the file is trusted.

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Andrew Lockton
Chrysalis Design, Melbourne Australia