1. You can use FDM/FDMEE (I don't want to suggest EPMA, that is also an option), make changes there and push it to the cubes.
2. Depending upon if this is a BSO cube, you can use DATAEXPORT and it is faster. There a native export (right click on database and export data) in Essbase, however there is limited option to make changes.
3. It is not possible to do that via MaxL, you can try using API and then do a compare.
if you want consistent outlines then you could use Essbase Studio to do it from a source like DRM or relational
for comparing data between cubes use ODI to pull specific data or you could compare using Financial reporting with multiple grids.
Rather than using report scripts to move data you can also use the dataexport calc script command (BSO only) or MDX