'Is there a way I can include certain subdomains to GA referral exclusion list

So I have 3 sites

1: www.main.abc.com
2: www.subsite.abc.com
3: www.others.abc.com

So I want to be able to go from Site 1 to Site 2 without Google Analytics treating it as different sessions. But whenever I go from Site 1 to Site 3, it should be treated as different sessions.

Is there a way I can add just site 2 to the referral exclusion list and not the top level domain abc.com



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