If only the evaluation criteria have changed and not the Government's basic requirements for the work to be performed under the contract, then the competitive field remains unchanged. In other words, it does not appear any offerors will be competitively prejudiced by the revised evaluation criteria. Offerors should be provided the opportunity to submit revised proposals to address the updated criteria, and it appears that was done in this case. So yes, the Government can change the evaluation criteria, and offerors are provided the opportunity to revise their proposals accordingly.