I don't think these grass EVER go fully dormant, so spraying a non-selective weedkiller like Roundup on the weeds is not a good idea. But it's easy to make a weed wiper to kill the offenders without hurting the lawn.
Wrap an old towel on the end of a garden rake and spray it with Roundup until damp. Wipe offending green clumps with the towel and no herbicide will drip down onto your lawn grass.
