the way to move the merged tag is, as you say:
cvs tag -RF TAG_NAME files to tag
so, as you've committed the fix for 18_STABLE and 19_STABLE (and HEAD), you need to do:
cvs tag -RF MOODLE_18_MERGED edit_field.class.php (in the 18_STABLE branch) and
cvs tag -RF MOODLE_19_MERGED edit_field.class.php (in the 19_STABLE branch)
to have both MERGED tags properly moved to the last version in each branch.
(Minor note: I think the "R" option is for "recursive". I don't use it really, because one mistake can cause ALL files to be wrongly merged. Just one comment).
About the other typos, yup, the "$tableparm" is Ok... but the "$rec"... it's an object and not an array, if I'm not wrong. Feel free to commit and merge. Assigning to you! Thanks!