In the RDBMSes I'm aware of, you can disable foreign key checks while still adding the constraints themselves---they won't do anything as far as the DBMS is concerned, but can presumably still be picked up by whatever tool you are using to generate this link information.
You usually can for maybe a table, or just overall. But I don't think you can specifically for one FK. This is mostly just a small pipe dream I think :')
No, in all RDBMSes I know of, it's absolutely the other way around: Enabled or disabled (usually CHECKED / NOT CHECKED) is an attribute you set for each and every constraint, either at creation (where it usually has one or the other as default if you don't explicitly set it) or in an ALTER... statement.
