It’s a wizard, I don’t want to set such basic things every time I use a particular template. Instead, this information should be in TemplateData, probably three-valued: the template SHOULD NOT be substituted (default) / SHOULD be substituted / MAY be substituted (then show the checkbox). —Tacsipacsi (talk) 18:47, 13 February 2023 (UTC)[reply]
Since this wish is about the Template Wizard, which works in the wikitext editor, I wouldn’t display the checkbox for SHOULD/SHOULD NOT templates – if one wants to substitute a template which is not designed to be substituted (or wants not to substitute one that’s designed to be always substituted), they’ll still have the option to add/remove the prefix after closing the wizard, just like today. So it’s a MUST before closing the wizard, but it’s a SHOULD before saving the edit. (If it was about the VisualEditor template editor, that would be a different matter, as VE doesn’t allow toggling the prefix outside of the wizard.) —Tacsipacsi (talk) 00:43, 25 February 2023 (UTC)[reply]