From my knowledge, no. There is no way to rename the listed options in blockproperty tablet.
Something to wish for maybe.
If your in desperate need of it you could probably archieve it with a a lookup since there you can name every option. But you would not have the pulldown menu under each nominal size. You'd have to make one option for each combination of size and length.
As far as my knowledge goes, best of luck
Signature, sincerely... //Adam AutoCad LT 2014 Give Kudos where credit is due, Mark "accepted as solution" if the post solved your question.