Where:  Same folder as messages.yml (your GriefPrevention data folder)
File:   ResizeStart-backup.yml

The backup file contains your old ResizeStart value and a short header explaining that
ClaimSelected and ClaimSelectedTopLevel replaced it. After the backup is written,
ResizeStart is removed from messages.yml so the plugin does not use it anymore.
You can copy any formatting (e.g. color codes) from ResizeStart-backup.yml into
ClaimSelected or ClaimSelectedTopLevel in messages.yml if you want to keep it.
 

ClaimSelected
  When:  Shown when you select a claim corner and that claim has no subdivisions.
  Suggests: /claim abandon to delete the claim.
  Default: "Claim selected. Use your shovel again to set the other corner and resize, or use /claim abandon to delete this claim."

ClaimSelectedTopLevel
  When:  Shown when you select a claim corner and that claim has subdivisions.
  Suggests: /claim abandon toplevel to delete the claim and all its subdivisions.
  Default: "Claim selected. Use your shovel again to set the other corner and resize, or use /claim abandon toplevel to delete this claim and its subdivisions."
 

/gpreload

# Master switch: false = no alias system, use default English command names
enabled: true
# Standalone commands: false = only /claim and /aclaim (or their translations) exist
# No /trust, /trapped, /abandonclaim, etc. – use /claim trust, /claim trapped, etc. instead
standalone: true

commands:
  claim:
    enable: true
    commands: [claim, claims]   # /claim create and /claims create both work
    # ...
  aclaim:
    enable: true
    commands: [aclaim, aclaims] # /aclaim restore and /aclaims restore both work
    # ...