Yes, providers may amend documentation for omissions or corrections, whether ROS, exam or any other documentation. There are specific requirements for amendments in the CMS claims processing manual.
https://www.cms.gov/Regulations-and-Guidance/Guidance/Manuals/Downloads/pim83c03.pdf section 3.3.2.5
The potential issues with amendments is if they appear to be created simply to justify a higher level of service. That would be fraud. But if the day after the visit, the physician is looking over a patient's note and he/she realizes they performed a cardiovascular exam and forgot to check it off in their EMR, they may do so as long as it is clear it is an amendment.