I don't know the rules for IDPA or IPSC, but USPSA Production doesn't allow barrel switches. Thus, they would require a complete upper change, not just a LWD barrel. The porting holes in the slide represent a cut-out to reduce slide weight and I could imagine that being frowned upon.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face