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Can you change the default column type from Single line of text to Person or group on the User Fields in List Settings?
No you can not change Single line of text to Person or group.
But you can change it to
Multiple lines of text
Choice (menu to choose from)
Number (1, 1.0, 100)
Currency ($, ¥, €)
Date and Time
Yes it can be change. Get into the column properties and change it.
Required, but never shown