I have seen this many times, specially when trying to prolong clutch releasing bearings when no replacement is available. Bearings like those can't be easily re-greased, like tapper rollers for instance. The procedure I have seen is by heating grease in a can, enough to soft it but not to completely liquefy it, then toss the bearing, stir, push the grease into the grooves, etc. and then let everything get normal temperature. It is said that it effectively puts grease "up to the most obscure corners" inside a bearing. They call this "cook the bearing". My question is: how would doing this affects the grease function in real world, not in theory?
The effects will be heavily dependant on the type of grease being heated so this is not a question that can be answered.
Usually bearings like that are filled by pressure from one side.
I have always had success by squirting in gease with a grease gun and rotating, then repeating squirting and rotating until the bearing was as full as possible. Worked fine on both small 1” bearings and saw engineers doing exactly the same with bearings of 15” diameter.