The 17 Sport has its own portsmouth handicap rating separate from the 17 SE, so you could use the jib for open class racing.
For one-design racing, I guess you technically need to convert everything over, but really, you'd probably be fine at the local level racing it as-is but without the jib. We have a guy that did that for a while in my area - he used his boomless mainsail and didn't use the jib (he has subsequently gotten a boom). Not having a boom or rotator is a disadvantage, so no one is likely to protest you. If you have the Harken main traveler, you might hear some grumbles, but more than likely, people will just be happy to have another boat on the course.
Thanks for the input.