BACKGROUND: The OPTIMIZE trial is a multi-site, comparative effectiveness research (CER) study that uses a Sequential Multiple Assessment Randomized Trial (SMART) designed to examine the effectiveness of complex health interventions (cognitive behavioral therapy, physical therapy, and mindfulness) for adults with chronic low back pain. Modifications are anticipated when implementing complex interventions in CER. Disruptions due to COVID have created unanticipated challenges also requiring modifications. Recent methodologic standards for CER studies emphasize that fully characterizing modifications made is necessary to interpret and implement trial results. The purpose of this paper is to outline the modifications made to the OPTIMIZE trial using the Framework for Reporting Adaptations and Modifications to Evidence-Based Interventions (FRAME) to characterize modifications to the OPTIMIZE trial in response to the COVID pandemic and other challenges encountered. METHODS: The FRAME outlines a strategy to identify and report modifications to evidence-based interventions or implementation strategies, whether planned or unplanned. We use the FRAME to characterize the process used to modify the aspects of the OPTIMIZE trial. Modifications were made to improve lower-than-anticipated rates of treatment initiation and COVID-related restrictions. Contextual modifications were made to permit telehealth delivery of treatments originally designed for in-person delivery. Training modifications were made with study personnel to provide more detailed information to potential participants, use motivational interviewing communication techniques to clarify potential participants' motivation and possible barriers to initiating treatment, and provide greater assistance with scheduling of assigned treatments. RESULTS: Modifications were developed with input from the trial's patient and stakeholder advisory panels. The goals of the modifications were to improve trial feasibility without compromising the interventions' core functions. Modifications were approved by the study funder and the trial steering committee. CONCLUSIONS: Full and transparent reporting of modifications to clinical trials, whether planned or unplanned, is critical for interpreting the trial's eventual results and considering future implementation efforts. TRIAL REGISTRATION: ClinicalTrials.gov NCT03859713. Registered on March 1, 2019.