I do not know if acid would do it but if you try acid test it on one or two pavers before doing the entire patio. You might have better sucess with a very powerfus pressure washer if you can use it without washing out the base. As mentioned in the post above mortar is not very effective holding the pavers in place. Sharp sand or crushed stone is very effective keeping everything in place. My preference is crushed limestone if I can get it. The sharp angles and different sized grains are what does the job. If it were me, at this point I would leave the mortar in place and use the sharp sand or crushed stone as it washes away.
You might try some of the sealer right on the pavers as they are. It may darken the mortar and make it less noticeable. I am not big on sealers for pavers because you need to reapply it every year or two.