Edit: This is in response to @tr0tsky but doesnt address the initial questions/responses.
In the Gear Optimizer you can lock any piece you want and the optimizer will keep that piece fixed. Do this by clicking on the piece you’d like to lock and then selecting the piece you want there form the popup. A dotted border should be around that piece now, which indicates that it’s locked. If you hit “save&update” it will re-optimize around your selection. It should look like this afterwards (note: not a real example cause I’d never lock in those boots for real):
You can see that it’s keep the boots in (even though the gearing strategy predicts that they’d be a loss) and suggests which trinket to replace my velen’s with.