How do you get Brand and/or PR teams onboard with new messaging?

Involve them early, and involve them often.

People often construe a tension between brand and product marketing when in fact they're often part of the same team. To paraphrase Jay-Z to Nas during one of their epic rap beefs: Brand can come up with hot lines, Product Marketing will come up with a hot song, except that here everyone wins. Brand is one of the many outlets where your messaging can sing, but it has to start with a common understanding of what your product does and why it's different, which is the purview of Product Marketing.

WRT to PR, they're your absolute co-pilot on launches at that last mile. Give them the positioning, the customers stories, etc and a good pr person will work wonders. They can also be your co-pilot for the launch announcement or blog, so again involve them early and deeply. It goes back to trusting them to figure out how your news and information will play with specific media outlets and building that trust on a common understanding of what your product does, and in the case of PR, specifically what it doesn't.

One really interesting technique I have used is to start by writing a press release for any new major message update. Or for a major launch.

This puts the brand/PR team in an arena they feel comfortable in, and forces you to really refine the message for this audience.

Once you have a draft PR, get feedback from a few respected Sales leaders, and relevant PM leads.

Use this to develop a short message deck, and do messaging testing with some analysts in your space. They'll help you refine the message even further!

Similar to how you need to enable sales when you roll out new messaging, you need to enable your marketing partners as well, especially if they're part of a cross-functional launch. I encourage marketing to attend the sales trainings, but it's usually also worth doing a dedicate session with folks from all parts of marketing where it might be easier for them to ask questions. 

And remember it's always important to set the context around messaging or a launch. Especially if it's a more technical topic, spend time educating on the state of the market or the key audiences as a whole, to help set the context around why you're doing what you're doing. 

When you're crafting new messaging, it's always good to start from a framework that includes your benefit and positioning but also answers the question of why now. Substantiating the new messaging with statistics and key proof points also reinforces the strategy behind the change since there are external facts that support it. I also find it's important to walk through the framework with your brand and/or PR teams vs. just throwing it over so you can have a meaningful discussion about the messaging changes and even get their feedback. This helps them understand the why behind the change and the importance of it but more importantly, bringing them along the journey helps with buy-in and also ensures the messaging is on brand.