you have two or three options.
1. Import Data Doctor will recognize some features, so you can go through there and enable them for modification. I'm not an expert on this method, so can't offer much more there.
2. Flexible modeling in Creo 1 and Creo 2 will let you modify hole diameters on neutral data.
3. Additive modeling...just create another feature on top of the hole to add or remove material.
Joshua Houser| Pelco by Schneider Electric |Buildings & Business| United States| MCAD Tools Administrator
Phone: +559-292-1981 ext. 3490| Toll Free: +800-289-9100 ext. 3490
May you should have a look to
A decade ago, I attended a seminar where they demonstrated a proto version of their 3-matic software. They were able to add drafts and rounds to STL-versions of complex castings. They even could identify a round, remove it, add a draft and add the round again.
I lost contact with them, so I've no idea if they brought and kept it in production.