[LUAROCKS] How do I install a rock for a different version of Lua?

[Dirk Laurie <dirk.laurie@...>]

I apologize, but not very sincerely, to those who deem LuaRocks user
questions to be off-topic on this list.

If I understand correctly, LuaRocks 3.0.x has a directory management
structure that allows rocks of the same name for different Lua
versions to present at the same time without interfering with each
other.

I currently have installed:

LuaRocks 3.0.4, the Lua package manager
CONFIGURATION
        Lua version: 5.3

I'm using an application that has a hardwired Lua 5.1 interpreter for
running Lua scripts. I wish to install a 5.1 version of a rock that I
regularly use in its 5.3 version. I can'f figure out from `help
luarocks` or 'help luarocks-admin` how to do it.