It can be fixed and it won't be visible once the trem and rear trem cover are in place.

The insert was still very firmly fixed and took a fair bit of removing. You either need a proper stud puller for this (easiest way), or you'd need to clamp some support underneath the insert positions as there's only 1mm or less between the bottom of the insert and the other side of the trem cavity, so the 'smaller bolt down the hole and wind away' method won't work without that. Even then it may well poke a hole through the bottom in the process.