I believe currently it is hardcoded to P/N or +/- (but not mixed!). That’s generally consistent with other packages, so it mostly works.
From my perspective, adding adjustable logic to associate nets as differential pairs is a fine addition, could absolutely be a feature request.
For me though, an additional option would be the ability to add “flags” to the schematic that allow for visually setting special design rules and other special features like differential pairs, regardless of net name. We use them as hacks for PWR_FLAG, but I feel like they could be more useful (in the style of Altium).