R13 D exempts all software and designs with source files publicly available before kickoff from not being allowed if designed before the season.
So as long as you post the source files, which in this case would be the CAD files to Thingierse, CD, or some other public location before the season starts you are free to use it on your robot as a manufactured part.
Without doing that you would either have to meet FIRST's criteria for a vendor, in which case your team could get one and use it as a COTS part, or make another improved version after the season starts. The latter option is allowed by Example 1 in the blue box for R13, but you'd probably need to make some significant improvements if you were to go this route—making small or pointless changes would be questionably legal and likely frowned upon.
Granted, this is all assuming that the whatever the equivalent of R13 is next year is the same. We won't be able to say for sure until kickoff.