I-2021
If you insert a speed constraint in the missed approach routing the aircraft will accelerate to that speed, so you can keep speed managed, i.e you need to fly 175 kt for go around, then insert 175 kt as a speed costraint. If you pull speed during the go around you exit the SRS and you go in OP CLB.
If I'm not mistaken, during a go around the airplane will ignore all speed and altitude constraints. Managed speed will be Green Dot speed, until the airplane is out of the Go Around Phase (either by activating App Phase or ENABLE ALTN).
See FCOM 4.05.80