Requested to add a tenant mid-lease. Yes / No?

[Aaron Ziegler]

Hello BP community, this is my first post as a new landlord. I'm excited to have started this journey and would appreciate advice or examples and outcomes. For reference, I live in the same small Montana town as where this rental is located.

I recently purchased a single family house and turned my existing single family house into my first rental. My new tenants are a couple in their early 20s and I was asked if one of his friends (male) whos lease ends elsewhere in November could move in with them and be on the lease. I explained that only this couple is on the lease and can live there, that nobody else could, but I would look into options about this as I am brand new to being a landlord. 

My initial thought is no. I'm not sure if asking for a higher collective rent and rewriting a lease to include this person (who I have not vetted yet) in November could be a good thing for more cash flow or if its not worth the risk? More money was never discussed, and I did not say yes or no, but rather that I would look into it. 

I also hesitate to alter the dynamic of a young couples household by adding a third person to it because it has a potential major effect on a relationship. Even though there's a potential for increased cashflow, I'm not sure the risk would be worth it?

I'd appreciate any advice on this. Anyone that has done this, what was your outcome and would you advise yes or no?

Thanks in advance.