Are there any ways to challenge these actions or demand a full refund based on the change in circumstances?
You need to ascertain from the community college the procedure for refunds, grievances, and appeals (not sure why a comment in this direction was removed or withdrawn). This information very likely is outlined in the school's catalog and akin sources. See Raethz v. Aurora university, 805 N.E.2d 696, 699 (2004) ("a college or university and its students have a contractual relationship, and the terms of the contract are generally set forth in the school's catalogs and bulletins", citations omitted). Although the college's belatedness of the new requirement contravenes the binding terms, your non-compliance with the procedural rules could prevent you from escalating your claims to [small claims] court.
From the standpoint of substantive law, you will need to advance the argument that you are entitled to void the contract (that is, pursuant to campus activities) on grounds that (1) you reject the college's belated alterations of the terms & conditions, and (2) the college concealed from you information that is material enough for you to decide whether to enroll in the course(s). Voiding or rescinding the contract implies your entitlement to the corresponding refund.
Since the Covid project/mess ensued long before the start of the current academic period, the college's cannot reasonably allege that its belated requirement is due to "unexpected" circumstances. The college's duty to timely and properly disclose said requirement is germane to chapter 23 of the Illinois Administrative Code 1030.60(7) in that requiring the student to take Covid tests is "likely to affect the decision of the student to enroll".
The college knew or should have known that a significant portion of the population is skeptic about the "pandemic". The college's deliberate pre-enrollment omission that it will require Covid tests for campus activities suggests that it knew such requirement might be "material to prospective students' decisions about whether to enroll". See Abazari v. Rosalind Franklin Univ. of Med., 40 N.E.3d 264, 276 (2015). That omission by the college constitutes a material misrepresentation on which you reasonably relied. Accordingly, the contract is voidable by you. See Restatement (Second) of Contracts at § 164(1).
If you end up filing a grievance and subsequent proceedings, be sure you read the Abazari opinion. Regardless of whether the court's portrayal of the plaintiff's arguments is truthful or distorted, the opinion showcases various mistakes a litigant is prone to make in the pleadings and subsequent arguments.