We can't assume that any given hotel network is well-configured, but most enterprise networking equipment verifies the source of multicast traffic against the multicast routing tables. This means that if you simply send packets with a source address matching the real multicast source, the network devices will ignore and not forward them. This reverse-path check is a standardized part of PIM, the most common protocol that network devices use to communicate multicast groups between each other. It's also enabled by default on Cisco devices for local groups and I would assume the same of other vendors.
That said, it's considered a best practice (although not really all that common) to use ipsec or another method to provide cryptographic authentication of multicast packets. The protocol discussed here may do so.
This reminded me of an evil prank I did on some friends of mine when in university - CD burners had just become a thing, and at the local concert venue where we volunteered, a handful of burned CDs soon appeared at the mixing console with various music the engineers liked to listen to while getting ready for a gig.
Anyway, I ripped the discs, added a nice 50Hz hum under the music and burned new copies which I then left by the CD player.
Yup. Cue frustrated sound engineers trying to debug the ground loop which only manifested itself when the CD was playing.
I never dared admit to the prank, but rather swapped the hum CDs for the originals before someone got a chance to investigate this thoroughly...
