Voltas less than one bar in length

I transcribe traditional (usually Scottish) music from old sources. Anacrusis is common and is a fuss where there are repeats, but the following strain has a different introductory note or notes than the preceding. Of course I can insert whole bars as voltas, but I could save a lot of space and time if I could mark just the last beat of a bar (say) as changing on the repeat. Is this possible?