You could plant out Thyme after growing it from seed in plugs.

Two issues you might want to consider are - weed control while it becomes established; and bees visiting the site when the plants flower. This may be a problem for pets and people sensitive to bee stings.

If you can establish it before the onset of hard, dry weather then it has a fair chance of spreading to cover the patches between the plantings, particularly if it receives only light foot traffic.

If your current groundcover is tough and vigorous then your first task is to clear it completely. If it is suffering from compacted soil or shading for long periods during the day then you may have to rethink the Thyme project. It will not do well in too much shade or competing with leaf litter, roots, and drip areas.