The Hallelujah chorus is a pretty ambitious work for most choirs, and generally requires intensive and prolonged rehearsal, and "musically educated" members in the choir, for an impressive performance. The tune tends to get deeply imbedded in the minds of the singers, with the result that I've heard individuals "spin into" random lyrics, some fairly extensive, to the tune. I have heard numerous "alternative" applications of the tune, although few that were particularly memorable.

(A number of the "near classics" definitely were not suitable for performance in sacred places.)

The Olivet to Calvary (with Hosanna chorus) is another to which I've heard "alternate lyrics," although it's a more complex tune that would seem to require some actual "development" to fit a narrative to it. A choir member of my acquaintance claimed an original lyric in the folk "37 versus with choruses" tradition, set to the OtoC tune, although I suspected some partial plagiarization from other sources.

Bottom line - someone may have published a "Hallelujah Happy Birthday" in which case there could be a question of copyright; but unless it's been "marketed" it's unlikely that you'd run into an "assertion of rights" for casual performances. Someone with access to the numerous choral music publishers might have a better chance of finding whether there has been a publication.

(The Hallelujah sounds a lot better than the "alternates" used by a number of franchise kid food restaurants - i.e. MacD and BKing etc.)

John