The process is fully reversible, I did it back and forth several times to made this document.
Use this script to Re-Partition back to 1GB System,
https://mega.nz/#!ax8C3bwS!IEMA-FP31chdmUfy48_nzDKRDGObrkCvMNFbzFSLmLk
Procedure is same, just replace 2GB_script with 1GB_script.
By the way, after Re-Part back to 1GB_system, Install MIUI8 will show error...., install MIUI7 instead
Above 1GB script will RePart system back to 1G, more preciselly speaking, it's a 787MB system...Exactlly same as factory default.
Detail 1GB/2GB system partition size:
https://mega.nz/#!ThckVSBS!VwhHmgj8oionzRHtdOPOxKho11zT-7rwkhKfVUAxxMk
https://mega.nz/#!K9dizIyJ!qED-t9M6gNPL6kOCzFOh7FJKE8B6QE6jXxRIPYtJ46c
I do not have a script to RePart system as 1024MB, it's enough for MiUi8 (see above 2 pictures.)
If someone can provide a 1024MB RePart script, it should works also