Can I use 6mm threadless topper on a 7mm back

I just had a check up for my second lobes, and they switched the backs from 8mm to 7mm. I am now allowed to change the toppers/stud, just not take them out. I can't find 7mm long posts though only 6mm or 8mm. Will 6mm work fine with 7mm or will they fall out?? This is threadless and I think they are 16 gauge