Is possible to revert a Grass Path to a Grass Block without removing it?

Solution 1:

Without removing, you can convert them to dirt by placing any solid blocks on top then removing them. Then you can place grass blocks anywhere within 3x5x3 box around the block you want to convert to grass, e.g. place some grass blocks 1 block above the dirt.

An especially friendly block for this procedure would be the slime block, as it's instantly placed and broken. Just place a layer of slime over the path, a couple grass blocks scattered on top of the slime to 'seed' the grass, then break the slime. If you like to live dangerously, TNT block has the same properties, just better not have any sources of redstone signal or open flame nearby.

A quick way to convert arbitrarily long flat strip of path blocks up to 10 blocks wide to dirt (then seed some grass blocks to let it convert back to grass) is using a flying machine:

You start the machine by triggering the "rear" observer relative to direction you want it to travel.