The Madcow routine can be modified to be consistent with Texas Method principles by setting the Monday ramp settings to 0%. That way you get sets across instead of pyramiding up. There's your volume day. Next up is recovery Wednesday and Friday is heavy triples.
Always record the absolute weight lifted. So if you are doing pull ups with 20 lb strapped around your waist, record that as body weight + 20. Alternatively, if you are using the pull up assist machine with 20 lb, subtract off 20 from your body weight and record that.
The weight lifted is not zero so don't record it like that. Use a suitable fraction of your body weight instead. 50% is a nice, easy number to work with.
After backing up to iTunes, your raw files are available through iTunes file sharing. If you'd like to manually edit some data the file to look for is the history.xml file. PR's, Load, BW, and BF are the entities you'll probably be interested in. You can edit those but be sure not to wind up with different counts for those four entities otherwise you will cause a crash when restoring.
Copy the debug.sbz file in iTunes file sharing from your source device to your target device. Use the "Restore from iTunes" function on your target device. Done.
You have two options for dealing with fails: 1) let Multi-Year work it out or 2) deload manually according to what you think is best. Multi-Year uses a more up to date method of dealing with fails that differs in each program.
Put simply, deloads will happen automatically after a fail and will be scaled according to the severity of the fail. Missing only a single rep might not result in any weight reduction whereas missing five from six will result in a more substantial drop in weights.
This scaling keeps the weights always relevant. The rest needed to recover and break through the plateau comes not so much from a weight reduction then but from a volume reduction (again, according to circumstances). You might find your sets dropped down to one after a couple fails.
While this system is more complicated than using paper and pencil, it's nothing for a mobile app to work out.
Of course you can always adjust sets/reps/mass to what suits you and use the manual deload option to drop back 10%.
It's your choice.