Click on "Start"
Type "CMD" in the "Search Window" (DO NOT HIT ENTER)
"cmd.exe" with a black ICON should appear in the Window above as the only result
Right Click and select "Run as Admin"
Type the following and hit Enter to see list of commands as I'm not sure if I remember correctly!
bcdedit /?
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I'm almost certain the following will change the text as you requested:
Type the following command in the Command Prompt Window exactly as you see it:
bcdedit /set {legacy} Description "Microsoft Windows XP"
Press ENTER
To exit the Command Prompt, do not use the "X", instead, type "exit" and press Enter!
If you want XP to be the default OS, use the following command:
bcdedit /default {legacy}
Press Enter
Exit the Command Prompt.
Let us know if it worked for you.