Yes, you can apply for a UPOU non-degree program or course (CEP or MOOC only) even if you are enrolled in another degree program from another university.
In the case of a UPOU applicant who is applying for PTC and another UPOU program, both applications can be processed. If both applications are approved by the respective program admission committee, the student should choose which program they would pursue in the University. If they should choose to pursue PTC, they should be considered as non-degree student and should not be allowed to apply for a degree program in the University unless, they would sever themselves from the PTC program. Severing from the PTC program should be done through a clearance.
For current students of UPOU programs, they need not apply to PTC if they wished to enroll in PTC courses. They can enroll in PTC courses as extra courses of their program in the University. However, their enrollment to the PTC courses should have a prior approval from both program chair of their degree program and the program coordinator of PTC.
Check the admission/enrollment/registration articles about these non-degree programs/courses: