Retrofit cavity tray workaround blown-in insulation with no adhesive

Yes you can fit a retro tray on pumped insulation if some falls out you can put Rockwool back in

If i were you i'd drill a few holes and spray some expansion around the area which should hold it back a little...im tempted to say expansion yet i think if you got 5 litres of pva and watered it down so it was runny...drill holes well above the lintel around 450mm and squirt a good amount in all holes and by the next day should be good to work...its an idea anyhow which should stick particles together. If it fails i would try an amount of both so pva first and finish with a blast of expansion. Some blown insulation is crazy the way it just cascade out and the thing is once its dislodged you might not see the void higher up the building...

Replace insulation with knew one also use dpm onp Cavity tray