As long as they can still get blood from other creatures too, I'm okay with it. If not, than that could have wild implications to the food chain assuming it leads to massive population degradation.
Not all species of mosquitos feed on blood, like how only some bats feed on blood. As long as we only mess with the ones that feed on blood, it is a lot more likely that species that feed on mosquitos will have time to adapt to population changes.
Even the ones that do feed on mosquitos don't feed exclusively on mosquitoes.