I have not configured and tested NCS 540 with multicast over segment routing, but... support is documented for the 540 (virtually the same docs as ASR9K link above):
https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5xx/segment-routing/710x/configuration/guide/b-segment-routing-cg-710x-ncs540/segment-routing-tree-segment-identifier.html
"Tree Segment Identifier (Tree-SID) is a tree-building solution that uses a Segment Routing Path Computation Element (SR-PCE) using path computation element protocol (PCEP) to calculate the point-to-multipoint (P2MP) tree using SR policies. Tree-SID uses a single MPLS label for building a multicast replication tree in an SR network. Tree-SID does not require multicast control protocols such as RSVP, mLDP, and PIM.
A P2MP SR policy provides an SR-based TE solution for transporting multicast traffic. It works on existing data-plane (MPLS and IP) and supports TE capabilities and single/multi routing domains."
As far as what XR code version to run: if you have an Advanced Services contract, ask for a bug-scrub on 7.9.2 to see if it has any show-stoppers for your use-case. If it does not, run with that; if it does, you can request a SMU fix for 7.9.2 (but a fix might not be SMU-able), or see if you can get the fix integrated into 7.10.2. If you target 7.10.2, take 7.10.1 into your lab for qualification testing and get any bugs you find filed before the commit window closes on 7.10.2.
Generally speaking, for XR. a ".1" release should be used for lab trials and a ".2" (or ".3" if that throttle has one), should be used for production deployments. Newer ".2" throttles are usually better than older as they will have more runway left for support (ie, SMUs).
Disclaimer: I am long in CSCO
