When you publish an opportunity for service providers to bid for you can limit which service providers are able to make a proposal. Through the course of receiving bids you may wish to change any restrictions you put in place, for example, to widen or tighten the pool of service providers tendering for your work.
If you are adding restrictions, any service provider who has already bid will be able to see the opportunity and update their bid. They are still included. Other service providers who did not make a bid and who no longer satisfy the options provided by you to tighten the pool will no longer be able to see the opportunity and will no longer be able to make a bid.
If you decide to tighten the pool of service providers by restricting it to a list you choose, then any agent who has already bid must also be a part of that list. Service providers do not have to redo a bid when you go from open market to closed tender.