My second question lies in making these strings more complicated -- to the point of containing regular expression metacharacters.

tr/// does not support regular expressions:

Note that tr does not do regular expression character classes such as \d or :lower:. The tr operator is not equivalent to the tr(1) utility. If you want to map strings between lower/upper cases, see lc and uc, and in general consider using the s operator if you need regular expressions.

Obviously I need to escape them,

If you do end up using s///, you can escape the regular expression using quotemeta.

Is there a default module which does such escaping, or is there a CPAN module which does what I need?

Probably. Can you show more small examples of what you are trying to replace?