As a general rule, employees are employees at will in Colorado, unless otherwise provided, which means that you can be fired at any time, with or without cause, for any reason other than those prohibited by law (e.g. race, gender, religion, whistleblowing in some cases) including a few reasons particular to Colorado law rather than federal law, such as sexual orientation, legal off-duty conduct in certain circumstances and voting. (The main exceptions are employees with written employment contracts usually in senior management, unionized employees and civil servants, which sometimes also limit schedule changes.)
If you are fired for cause, or quit, you are not entitled to unemployment benefits. But, if you are fired without cause, or you are "constructively discharged" then you are entitled to unemployment benefits. A "constructive discharge" colloquially speaking, means that conditions were made so bad for you that you were forced to quit.
There are also no rules limiting changes in schedules, assuming that each schedule allocates you the break time mandated by the Fair Labor Standards Act, and that you get paid overtime is you work sufficient hours to qualify for it under the Fair Labor Standards Act.
It is conceivable that frequent changes in schedules could cause a "constructive discharge" although I've never encountered a case (personally or in reported case law) where that has happened because it is quite unusual behavior for an employer.
Ultimately, the logic of employment at will is that if your employer is not good to work for, that you should seek employment with another employer who is more tolerable. Similarly, an employer constantly behaving in an unreasonable way may have trouble holding onto employees.