Thanks for the reply, command association.
Your question was general, and with that, it is often complicated to find a one-size-fits-all solution, s we all have our ideas of where it would stop working.
If you have a specific case, then please share that as a sketch or as a file.
My typical MO is that I love seeing the Project file or a sketch.
I do not like to answer questions or reply from memory. Over the past 17 years, running the Q&A forum here has proven to be the best way. This thread shows that not having specific data is wasting your time. Sorry about this.
I love to find creative solutions if there is no default option.
One question, why it has to be a Spline? What is the target? The more details you share, the better I can explore this.
Cheers