There are a few things you can do depending on the type of inserts you have. Inserts are 8/32 thread and some are threaded all the way through and some just have a hole in the back end and the threads don't extend all the way through. If your inserts are threading all the way you can take 8/32 set screws say 3/4 or 1 inch long and thread them in first with blue threadlocker, then screw your field points or broadheads on. Make sure to thread them in the same length, measure insert first and don't run them all the way through. Second you may have to modify your inserts by opening up the end and re tapping and will have to remove them to do so. Third Gold tip makes a stackable insert weight system you can buy in 10 and 20 grain weights. Others options are like you mentioned are brass inserts and they also make 10 grain washers you can add under your tips, but can only add probably two washers or you will not have enough threads in your insert.
The older I get the better I was.