“a hold keyframe keeps its value exactly the same until the next keyframe”
Yeah, you make the first keyframe, set your parameter values as needed, then put the playhead where you need it, without changing any parameters you simply make another keyframe, simple. No need for anything special. As long as you’re not changing parameters between them, it’s a “hold” keyframe. All keyframes are “hold” unless the next keyframe changes a parameter. Simple.