When I write a purchase agreement for my buyers and send it over to the listing agent, there are a lot of times when we'll negotiate back and forth to hammer out all the details. Then we'll re-write it so it's "clean" and not written on and crossed off.
The only thing that this would effect is if another offer that's better than yours comes in before the offer is finalized and signed by both parties.
I wrote a quick blog about this. Check out the link below.
It is common to get verbal inquiries regarding an offer to see if the parties have common ground on various details. Moving the discussion to writing as quickly as possible reduces the chance the deal will fail or details of the discussion lost.