RoboHelp's Multi-File Find and Replace (in the Tools tab)
should be suitable for this job, and you can control each
occurrence as you choose. (Where this RH utility fails is when your
search string might sit on more than one line, which won't be the
case here.)
You'll run two replacement passes (spaces added to < &
> tags for proper viewing in this forum):
Replace < h2 > with < p class=YourNewStyle >
Replace < /h2 > with < /p >
The < h2 > and < /h2 > strings will never be
split between lines, so RH will catch every one.
BTW, Add me to the list of FAR boosters; it'll let you change
case, change file names, etc., etc., etc. Great tool!
Good luck,
Leon