It would be more helpful to learn and/or advance your OMM skills in the setting of a residency that encourages training and practice of OMM (OMT). You can go straight into practice using this medical tool if you choose.
It is possible to advance these skills after residency but to start from scratch would be difficult and time consuming. Likely, much more difficult as the time pressures from family medicine practice will limit your ability to take OMT CME plus all the rest of medicine you will need to keep updated.
With that being said, you must seriously look at what family medicine programs accentuate OMM. Many of the DO programs won't and if going into FP, a strong FP program overall is vital.
There are a few allo residencies that support DO and MD development of OMM skills. I'm in one now in TN.
If you are DO and truely want to use OMT as a large percentage of your practice. I would suggest looking into OMM residencies or OMM fellowships after you finish your residency.
Good Luck.