Moving around the three day program

Sorry if this isn't the place for it, but i had a couple questions.

I use the old numbered programs spreadsheet.  I'm almost done with my first round of sheiko now and am feeling pretty good.  After finishing up a shortened 32, I'll restart at 29 with new maxes.

A couple questions on modifications for round two... 

1)  I have a hard time being able to spend so much time in the gym.  I'm usually a pretty slow lifter so that adds to it.  I've been missing a lot of assistance and added back work.  Anyone add a fourth day for some extra chins (5x5), rows (3x8), and light leg and chest work?

2)  On days where there are two 'blocks' of squats or bench, has anyone swapped out to a variation for the second 'block'?  I'm thinking of doing front squats (70%ish) and maybe OHP or incline press instead of the second 'block' of squats and bench.

1)  I have a hard time being able to spend so much time in the gym.  I'm usually a pretty slow lifter so that adds to it.  I've been missing a lot of assistance and added back work.  Anyone add a fourth day for some extra chins (5x5), rows (3x8), and light leg and chest work?

I have experience with a 4th day to the 3-day a week program. I used the light day as an way to progress to a 4-day a week program. Used to do light deads, light bench-stuff and back work out/support. But if you problem is that you start missing some of your work-outs maybe this is not the solution. If you are restricted on time maybe you should modify the program so you don't miss anything you are scheduled to do.

2)  On days where there are two 'blocks' of squats or bench, has anyone swapped out to a variation for the second 'block'?  I'm thinking of doing front squats (70%ish) and maybe OHP or incline press instead of the second 'block' of squats and bench.

Yes to that as well.
If for instance you are doing:
Squat
Bench
Squat

You could do (an example):
Squat
Bench
Squatting with chains