I’m not a member of a party, but I follow politics, and here’s how I understand it happens in Canadian parties.
In addition to leadership conventions, the parties also have policy conventions, where they debate policy proposals, annually or biannually, depending on the party. Each riding (constituency) association can send proposed resolutions, and also send delegates to the convention. The convention debates policy proposals from the riding associations, and depending on the party rules, there may also be proposals from the floor. The resolutions that are passed go into the party’s policy book.
That doesn’t necessarily mean that the party will campaign strenuously on all the policies in their policy book. The campaign committee, the party leader, and the incumbent Members have the major role in choosing the campaign planks, based on what the party membership has put forward, and also their view as to what makes for a good campaign, based on their experience on the campaign trail.
So, the rank and file has influence on the campaign, but aren’t determinative. On the other hand, if the leadership snubs the party membership’s policy proposals and takes the party in a markedly different direction, that results in lost memberships and loss of door-knockers.
If Ultra Vires joined the local conservative party riding association and paid the membership fee, he then could participate in proposing resolutions from that association. If he’s persuasive enough, the riding association policy committee might agree with his proposal and send it to the party convention resolutions.
Then Ultra Vires could put his name forward to be one of the riding association’s delegates to the policy convention. Maybe there’s several folks who want to go, and he has to win a local vote. Or maybe there’s not many interested and the association is glad to have a volunteer to fill their slate of delegates. Depends on the dynamics in the association.
If he goes to the convention, then he has to try to get people to back his policy resolution. Best to start working the phones well in advance, calling other like-minded delegates from other riding associations, to try to build a core of support for his proposal.
Sometimes there’s so many resolutions that the convention’s resolutions committee weeds out the ones that don’t seem to have much support, so it helps if it’s not just Ultra Vires pushing for it. Depending on the size of the convention, if the resolutions committee passes it, it might go to a subject-matter committee, where similar resolutions are grouped together. Maybe Ultra Vires’s résolution gets sent forward to the plenary. Or maybe there’s a similar resolution that appears to have greater support and it goes forward, and Ultra Vires has to decide whether he’ll support the similar resolution.
Finally, if it reaches the plenary, Ultra Vires and his supporters that he’s built up will make the case for the resolution. And they’ve probably been talking it up in the various committee stages and the hospitality rooms, trying to garner support. Maybe it passes and becomes party policy! Or maybe it’s rejected, but by a close enough margin that encourages Ultra Vires to keep trying to build support for next time. Or maybe it’s defeated by a strong vote against, and it doesn’t look worth trying again.
So yes, as a party member, you can try to develop policy and shift the alignment of your party. But you’ve got to be prepared to put work into it. This is classic organizational politics.