"Macintosh XL" is a term with complicated meanings: that is, it was a marketing term
At one point Apple sold Lisas running the MacWorks software (but with no hardware changes) as Macintosh XLs. My Lisa 2/10 is this way: its owners manual has
a sticker of a Lisa rendered in the Macintosh "Picasso" style that says "LISA IS NOW MACINTOSH XL".
Later on, you could get machines with modifications that made it impossible to run Lisa operating systems and software anymore, most notably the "square pixels" modification
@nekonoko mentions that changed the screen resolution. To a few people, this is what really makes a "Macintosh XL", although I don't think Apple saw it that way. Still, this is bit more serious than marketing perhaps --- although now that the Lisa OS+apps source code is out there, presumably you could update them to make use of the changed screen resolution.
In any case, depending on how you look at it: I have a Macintosh XL when I boot it into MacWorks, and I have a Lisa when I boot the Office System. But nobody's really keeping score...