It's easy to have a computer based system (which is all that arrangers are, these days) differentiate between styles made in their entirety by a user, and a style made from parts of purchased styles. Basically, all it would have to do is 'flag' any style the user makes that includes protected style components, and not allow it to be exported.
You would basically have a system where the style is 'keyed' to your specific hardware, and you can edit it, use it to make other styles, but any style that contains a third party style Part would be 'flagged', and not available on the export function.
Make the parts up yourself, no problem...
And, I'm sorry, but we have ALL seen the prevalent attitude towards styles here. Subscription, outright purchase, inclusion with the purchase of an arranger... everybody considers that, once they have 'bought' their styles, they are theirs to SHARE. And that's where everything falls down.
Only protected styles will remain on a 'one style, one payment' to the creator. I wish it were otherwise, but reading this forum's posts ought to make it obvious what the vast majority think...
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An arranger is just a tool. What matters is what you build with it..!