You didn't say if you have any status with any airline. Depending on your status, the answers and recommendations may be different.

I believe generally speaking, airlines will charge a change fee when you want to change the date of your award tix after ticketed. Routing change mostly likely is not allowed. You should check out the terms and fees under each airlines you have miles with and see which one will charges you least or give you most flexibility in terms of changes.

At least for UA, your routing sounds like a *Alliance tix. For *Alliance award tix, you not only have to call the agent to book it ($25 booking fee) but also change fee applies once it's ticketed. You may only change the dates on the *Alliance segments before departure. If the trip has begun, only segments on UA metal can be changed. The acceptable changes apply to dates only. You can't change routing. Link to UA rules: here. $150 change fee PER change with UA. However, being a UA 1K, the change fees will be waived.

Do the same research on AA & CO and see if your routing is possible.

You seem to require both dates and routing changes on this trip. If I were you, I probably will just buy the ticket to maintain the flexibility.

Good luck!