Yeah, that... No. Custom Lineage is one thing, swapping a proficiency for a proficiency is another thing, swapping an ASI for another equivalent ASI is also a thing, but swapping a proficiency for an ASI or a friggin' whole-ass feat is something entirely different and a frankly impressive leap of munchkinry.
In other news, the Grappling Strike battle maneuver specifies "melee attack", not "melee
weapon attack" as its condition for usage, meaning that shoving a creature counts!
...unfortunately, the condition is that you have to
hit with the melee attack, and since shoves don't involve an attack roll, it cannot technically "hit". So it doesn't count.
But this brings me to another, somewhat odd interaction/question. If you have that maneuver, a familiar, and a touch attack spell... When routing a spell through a familiar, is it *you* hitting with the attack, or is it the *familiar* hitting with the attack?
Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it. If the spell requires an attack roll, you use your attack modifier for the roll.
From the wording of "
you cast [the spell]", it would make sense that all related rolls and conditions/effects would relate to you, but you're just casting it from the familiar's space.
But "your familiar can deliver the spell
as if it had cast the spell", followed by the clarification/qualification of "If the spell requires an attack roll, you use your attack modifier for the roll" makes it seem as though it's the familiar who is making the attack, just with your attack modifier. Just like if you'd handed some pebbles from Magic Stone to someone else. They're making the attack, but they're using your ability modifiers for it.
So is the familiar making the attack, or are you making the attack from the familiar's space? If you're making the attack from the familiar's space, then you could technically cast Shocking Grasp and attack through the familiar's space, and then qualify for making a bonus action grapple on them via Grappling Strike (which admittedly would fail unless you're already within reach of the target that the familiar's zapping, as the maneuver just directs you to the rules on grappling).
It's... An odd interaction. And probably not very useful unless you're for some reason not capable of making attacks, or your familiar has some bonus to its making attacks. Or you're using flanking rules.