Event API in Plugins - Changing content before it's saved

I'm working with the In-Process Event API, hooking via ContentBeforeCreateEventHandler / ContentBeforeUpdateEventHandler.

This is triggering fine & I'm hitting my breakpoint in the C# code. I can see the contents of the fields via GetReviewableText, so that's working nicely.

The bit I'm stuck on is how to makes changes to the content before it's actually saved?

Here's a basic class showing what I have so far..

namespace Blah.Blah
{
    public class ContentRewrite : IPlugin
    {
        public string Name => "Test";

        public string Description => "Test";

        public void Initialize()
        {
            Apis.Get<IContents>().Events.BeforeCreate += new ContentBeforeCreateEventHandler(this.Events_BeforeCreate);
            Apis.Get<IContents>().Events.BeforeUpdate += new ContentBeforeUpdateEventHandler(this.Events_BeforeUpdate);
        }

        private void Events_BeforeCreate(ContentBeforeCreateEventArgs args)
        {
        }

        private void Events_BeforeUpdate(ContentBeforeUpdateEventArgs args)
        {
            args.GetReviewableText().Add("Body", "This doesn't do anything");
        }
    }
}
 

The GetReviewableText() method doesn't have much that I can see re. making changes to the submitted data, maybe apart from using .Add, but I tried that and it doesn't affect anything.

Am I missing something?



clarifying the title
[edited by: Matt at 2:02 PM (GMT 0) on Tue, Jan 12 2021]