High tier tomestones to low tier tomestones.

Hello.

Is there anyway to trade in high tier tomestones for low tier tomestones?

EG, Verity -> Poetics.

I've been capped on verity for awhile and have nothing to spend them on. If we could trade in for lower tier tomestones, even at a bad ratio, at least they'd always have a use.

Not at this time. There will be a time, a few patches from now when Verity become obsolete and discontinued. That is when you will be able to exchange them for another currency.
Currently Lore can be exchanged for Poetics and when patch 4.1 comes out, Lore will be removed from the game. The historic ratio is 4:1, so, when they do unlock the exchange your 2000 Verity will net you 500 Creation.

What might happen sooner, is when Omega savage is released, some crafting materials will be made available for purchase with Verity. So, at least you will have a use for them.