Create a baseline with individual tasks whose relevance is suitable to what logic you want the process to follow. Rather than a call from one action script to another, it would evaluate the relevance of the next task in the baseline to determine if it is relevant.
I’ve seen some RFEs for ‘reusable modules’ that can be called, however I haven’t seen it implemented yet. I hear what you’re saying and agree that the ability to reference other content items would be useful. However today I think we’re limited to baselines.