Hi,
I have not heard reports of this. But is possible.
Firstly if the grip is designed to hold the gun, yes you can pick it up using the pistol grip. That's a major function and should not fail.
In general with all manufacturers some parts may work loose, I have heard of other BP airguns with similar grips having loosening issues.
Maybe ask the RFD who sold you the rifle. They have a direct link to the importer / distributor and they can ask what the fitting is for the aftermarket possibilities. I am not aware of a big range for the Weihrauchs - but do ask.
Don't have a magic answer for this one, but always best to ask the retailer and they can get official advice. But things do work loose and maybe a characteristic of the gun.
Probably not the most helpful answer - but I did try. ??
G