I’m not sure if you’ve noticed, but (using the US as an example), the GOP is clearly driven by the voters, not the other way around. Donate all you want to the party, it doesn’t matter – the politicians succeeding are the ones pandering to voters. Notice how retiring republicans keep becoming much more rational as soon as they’re no longer running for reelection.

If you want policies to change, convince GOP voters it’s in their best interest.