If the channel change took place BEFORE the grant of your original construction permit, then your station would not be subject to any pledges and your station would not appear on the REC Pledge List.
If the subject LPFM station is not on the Pledge List, then this is not an issue as there is no obligation under the pledge and you can stop reading now.
An LPFM station will appear on the REC Pledge List if they were granted a Construction Permit based solely on their final score at the conclusion of the appropriate 90-day remediation window that followed the 2013 LPFM filing window. In other words, if an applicant was eliminated from your MX group because of insufficent points, at the time following the 90-day remediation period, the granted station(s) in the MX group would be subject to the pledges.
If an LPFM station is currently time sharing with another LPFM and that points had to be aggregated to eliminate another applicant (for example: originally a 4 station group, 3 5-point applicants and a 4-point applicant; two of the 5-point applicants reached a time share agreement and submitted that agreement during the remeidation window to aggregate their points to 10 and win the group thus eliminating the remaining 5 and 4 point applicants) and one of those stations decides to move to another channel and no longer be time shared, it is REC's opinion that this change does not relieve you of the pledge.
Even though you have moved to your own channel and no longer need the time share agreement, your station still eliminated other applicants during the original construction permit process and therefore used points to its advantage. Those points were predicated in part on the fact that the LPFM organization pledged at the time of application that it would maintain a studio presence for at least 20 hours per week and 8-hours of local programming per day (if those points were claimed). The fact that a Pledge List station even exists today was because of the leveraging of points during the initial construction permit process and therefore it would be logical that since you did use points to obtain your construction permit, you would be subject the pledge regardless of any changes that were made after the issuance of the original construction permit.
One thing to also consider where it comes to pledges and points, the FCC does not appear to be tracking those stations that are specifically subject to the pledges. There is no condition on permits and licenses (like there is with full-service non-commercial stations from the 2007 window) and there is no indicator in the FCC's official broadcast database. The REC Pledge List is an unofficial publication based on the outcome of the 2013 LPFM filing window. We do note that the LPFM stations on the Pledge List should stick with their pledges as it may come back and bite them in the next renewal cycle if they don't. Keep in mind that this does not mean they are not enforcing the rule however it may be possible that they may accidentally enforce it on a station that should not be subject to the pledge.