I covered this type of composer editing many years ago in the 6000 book, over several chapters step by step with many examples, for example:

First insert 4 new measures on to the end of the pattern, then copy the first 4 measures into the last 4 measures. Then edit the last 4 measures to make them different to the first 4 measures to make a brand new 8 measure pattern.

Now you could take an entirely new pattern track from the easy composer library for example, save it in composer C and copy the track from composer C to a single track, say accomp 5, of composer A making a new variation, using page 2 of the copy. Delete the first 4 measures of the new track leaving the new accompaniment playing for measures 5 to 8 for the new pattern, making the second half of the 8 measure pattern different to the first half.

Now if you want to add a new variation or fills on to the end of an existing variation it can be done on page 2 by copying track by track but only from within the composer so if you use accomp5 to input a new track copied in from composer B or C, you then copy the relevant measures to measures 5 to 8 of another accomp track in composer A, but accomp 5 then cannot be used in the same way without further complication of using further composers B and C because it has been used as the transfer path.

So you use the sequencer, play or step record one 4 measure variation followed by the other in C major, then APC to SMF convert all 8 tracks, then SEQ to composer copy the 8 measures. A new 8 measure composer of exactly what you require!

The disadvantage of the sequencer method is you lose the balance information, so just adjust the internal composer balances to their previous levels etc in the Composer Part Setting page, and possibly any dsps or digital effects etc.

This was described in the book putting automatic fills within the composer pattern so you don't have to press a fill button, but is just as relevant for another variation.