Can I use colace as a miralax (polyethylene glycol) replacement every day for chronic constipation?

Up to your doctor. Talking with your own doctor about this will yield more personalized results -- it looks like you've had quite an extensive workup of your GI complaints. Being on chronic laxatives is likely to be unhealthy for you in the long run. Colace (docusate sodium) is a stool softener, not a laxative -- but some say it causes cramping. Hoping you and your doctor can arrive at a helpful plan.
Colace (docusate sodium) You can use colace instead of miralax (polyethylene glycol). Although clinical trial showed MiraLAX (polyethylene glycol) to be more effective. Miralax (polyethylene glycol) is safe to use chronically. I would use colace on a needed basis. Best not to use medication chronically if you could help it. Eat high fiber diet and adequate hydration. Use citrucel, one tablespoon in 8 oz of water daily first before using medications.