The hardware needs to support it, this is the only restriction, as the software feature is included with the lowest license level (L2-Edge). Is that an original x450-24t, or a x450a/e-24t? I don't really recall for the original x450, but I think it has that capability.
VMAN is listed in the original x450 DS. Looking into the 12.4 Concepts Guide, in the Appendixes, x450 is listed as well for the following: - vMANs—Q-in-Q tunneling (IEEE 802.1ad vMAN tunneling standard) - vMANs—Egress queue selection based on 802.1p value in S-tag - vMANs—Egress queue selection based on 802.1p value in C-tag