Wait. If the changes are minor and involve product costs and are not major construction changes, you can have them factored in to the final contact after you select the contractor. There should not be change orders required if you specify them before the work begins, but you should expect to pay for any upgrades or additional labor costs as part of the final contract. If you bring them up now, the contractors may think you are indecisive and may factor extra costs into their bid, or decide they don't want the headaches of dealing with the potential for future changes.

And after you select a contractor, inform them of the changes, and they respond; when you have the final plans ready for permitting, they will be reviewed for any elec., cabinet and mechanical changes required. At that time, and if there are no further changes, a final bid and contract documents will be prepared.

I agree. The purpose of the bids is to compare prices as part of the contractor selection process, not necessarily to get a final number.

Make sure they are all bidding based on the exact same information, with as much detail as possible, even if you make changes later.

Change orders don't come into play until after you've signed a contract. Once you've selected your contractor, give him/her your final changes and ask for a revised bid as part of the contract.

Here is a link that might be useful: Comparing Contractor Bids