Questions regarding Refinancing part of BRRR strategy

[Renjason Patulot]

New RE investor here so I may be asking silly questions. 

1. Is the process for applying for refinancing different from applying for a mortgage to initially buy a property? Or are they pretty much the same and that they look at the same variables when approving an application? (e.g. credit score, annual income, credit-debt ratio) Is there such thing as a pre-approval for a refinancing? 
2. Once pre-approved, am I right to assume the amount does not change unless there is a change in my finances? (i.e. income, debt, credit score)
3. Can you refinance twice? For example, after refinancing you find a lender with better rate, does this happen and do people replace the original mortgage with a newer one?

I'm asking these because I'm thinking of buying property using short-term money, specifically hard money lenders for deals so I'm trying to look ahead into the refinancing part. I'm wary of entering a deal without being prepared to refinance.