The list of current policies which are wildly unjust or flat-out insane, and for which this strategy would have to be applied, is always much longer than the list of candidates. There are no US elections, ever, in which it is possible to vote for any candidate who would not have to receive a long list of such twitter posts. I don't see how this strategy can work.

In a republic that doesn't work. Citizens have one lever to control policy: vote for or against their representative. We see this all the time with statements like "I don't like X's view on abortion but I think Y's position on climate change is even more damaging so I'm voting for X."

Do you believe this will have an effect?

Probably not in the short term and only if enough people start doing it. I like the idea of making it clear for the people you're voting for and against why you're voting/not voting for them. Hopefully, it'll influence their future platforms.

If you contact your congresscritter over their official congressional channels - email, phone, Twitter, plain ol' letter - and tell them you plan to vote for/against them because of $X, a very polite intern will tell you that they will record your support/opposition to $X but that they cannot pass along your comment on voting to your congresscritter.

Be sure to share that with their campaign: that's how you get that message through.

They can't "pass along your message" specifically but when they get several hundred people saying they didn't vote for $boss because of their stance on $issue they will find a way to let $boss know about the pattern.