This does make sense --- and it's a request we've gotten from others. It's a good idea! In LSB 2.0, I half-way met this request. Here's how: when you plug hymns or readings into a Service and later change the Liturgy, Builder "remembers" the hymns and readings you'd picked and tries to plug them into the appropriate elements in the new liturgy.
So you could create a custom Liturgy with just "Hymn of Invocation", "Hymn of the Day", "Distribution Hymn", "Distribution Hymn", "Closing Hymn", plug your selections into those buckets and later on pick a liturgy which has elements with those names.
So, we plan on thinking through simpler ways of accomplishing this in future versions of Builder, but that's one technique you can use now.