Can bulges at l3-l5 weaken sphincter muscle and cause some degree of bowel incontinence?

Depends : Not bulges per say but if there is enough swelling to narrow and put pressure on the spinal canal you can have big problems and if you have bowel or bladder changer with back pain you should seek care immediately!

If significant,: However, it that is what is causing it, you need evaluated in an er and likely with an MRI asap. It is an indicator of compression and malfunction of the nerves, which can become permanent.

Bulges and bowels: Not likely. Bulges are not likely to cause many symptoms. In fact, using study data, bulges are actually more normal than not. So bulges do not imply any symptoms. You would need severe pressure on the nerves with obvious spinal stenosis (which could be aggravated by bulges if you had congenital abnormalities). So relax. May be a fissure, or other bowel issue that a GI doc would solve.