Nope, not with your current setup. If you're s-on you need to flash the boot.img with fastboot every time you flash a ROM. Don't even bother trying to boot into a ROM after flashing it without first flashing the boot.img via fastboot. If it has booted sometimes without flashing the boot.img, it's because the boot.img that was left over from the previous ROM is somewhat compatible with the new ROM you flashed, this is not optimal of course. If you don't want to have to flash the boot.img anymore, get s-off. Having s-off removes the restriction that causes the boot.img to not be flashed in TWRP when flashing the ROM.
Sent from my Evita
HTC Evita | KarbonKat 4.4.2 1.0-5
S-off | 2.14 | Modified TWRP 2.6.3
Do not PM me asking for assistance, that's what my Q&A thread is for!