Muriatic acid does lower the high initial pH of the water, but it does not provide COMPLETE curing (though it will provide some nasty chlorine fumes during use). That can still only take place with a certain amount of time... And like Daelynn has earlier suggested, any acidic supplement to the curing process can somewhat weaken your rock, especially the more delicate pieces. Just remember... no matter what methods you use or shortcuts you may take, please just keep checking the pH levels BEFORE introducing your rock into your tanks.
Personally, I'm just going to use the best process available (just like everything else we do with this hobby of ours)... time. What's six weeks compared to the piece of mind it gives knowing we're not introducing anything harmful to our little wet friends?
A "part" can be any measurable unit. One part (cup, lb, gallon, etc.) concrete... Five parts (cups, lbs, gallons, etc.) oyster shells.
Good luck and welcome aboard!