I have a mild-moderate cat allergy - wheezing, red itchy rash, coughing, stuffy nose, etc. In the past I’ve encountered cats that really send me over the bend.
However, now I have 2 cats. One is a 19 year old that used to belong to my friend - she couldn’t keep him anymore so I took him in, allergies be damned. Then my SO moved in with his cat - at first I was quite allergic to him, but Mr. Wonderland took care to brush him and wash him often.
Now I’m totally fine with both of them - no particular allergies at all. I am, however, still reactive to other cats.
So I think it’s possible to get used to the dander of a particular cat (or cats) and no longer have a reaction. Well, at least it was possible for me.