You can do almost exactly this with keyword bookmarks. The only change is that you need to put the "keyword" at the start of the URL. So @l linux rather than linux @l.
Create a new bookmark with these settings:
Name: Whatever you want.
URL: The search query you want with the text replaced by %s. For example https://kagi.com/search?q=%s+site:https://lemm.ee.
Keyword: The tag you want. Such as @l.
Now you can type @l foobar in the URL bar and it will go to https://kagi.com/search?q=foobar+site:https://lemm.ee. (Or whatever search engine you have configured.
Keywords can also be used for non-search bookmarks and javascript bookmarklets which are very convenient.
Yeah, it is sadly not advertised. Even the "Keyword" box helper text isn't very obvious how it works. They should link to a help page.
Not to mention that they also have search engines which work in a very similar way, but have a different UI, are harder for users to manually define and don't sync across devices via Firefox Sync.
It's a big mess. But it works! So that is enough for me.
YES THERE IS, THERE IS A TOOL FOR LINUX THAT TURNS KEYWORDS INTO WHATEVER YOU WANT THEM TO BE, I just need to find it again so hold on FOUND IT, IT'S https://espanso.org/
or you could use DuckDuckGo, its !bang feature lets you directly search on a website you want. searching "Beatles !mb" will redirect you to MusicBrainz' search results, for example.
Firefox has keyword bookmarks which is basically identical to bangs but you can customize them to your preference and they don't require sending your query to a third-party remote service.
Just set the "Keyword" option in a bookmark and type mykeyword foo in the URL bar to search using your bookmark mykeyword. I use a lot of one-character keywords such as m for https://www.google.ca/maps?q=%s, g for https://www.google.com/search?q=%s, d for https://www.dndbeyond.com/search?q=%s and similar. I also have a keyword e which runs a bookmarklet that fills in a one-time email into the currently focused input field.