I wouldn't cut unless you have a bunch of experience making trigger guards from scratch, joining the pieces back together isn't as simple as it may seem.
Bend it, I cold forged mine but the metal was so hard that a file would barely touch it. My butt plate was made from the same metal, when I couldn't get the toe to fit after weeks of work, I heated the toe of it red hot and smacked it with a hammer, perfect fit.
Worst case scenario, you break something and have to order another trigger guard, I have done that time or two on different gun parts, usually a nose cap.