My experience is that wire beaded tires tend to loosen with use, so used tires can be easier to get on the rim. However, when I was running Michelin ProRace3 tires on Campy rims, it was always a b!tch and a half to get the tires on the rims, no matter how old they were. Sorry, it was quite some time ago, I'm not sure if the tire had wire or kevlar beads, I've heard that kevlar bead tires do not stretch. Eventually I gave up on that tire/rim combo, I switched to Vittoria Rubino Pro Slicks. It was not that hard to get those tires back on the rim on the side of the road.
If it was me, I wouldn't ride without the tool unless I knew from experience that I could get the tire back on the rim without it. Speculation (especially speculation from people on the internet) wouldn't be good enough for me to risk leaving the tool at home. If you can't fit it in your saddle bag, can you put it in a jersey pocket? Handlebar bag? Frame bag?