So if Ukraine received AGM-88 HARM then it is capable of using it in that mode which requires only the LAU-118 launcher, some cables and a simple switch in the cockpit with a light indicating that the missile has locked on an emission source. This kind of work can be easily done in the facilities that repair Ukraine's fighters and could be installed on any aircraft that is capable of carrying 500kg payload on a pylon.
You still need to do separation tests and the like. You just can't sling weapons under a wing and expect the aerodynamics of the missile, the aircraft and their interactions with each other to just go smoothly on the first try.
Let alone fitting a HARM under a design never meant to carry them like a Flanker or a Mig