File opens in HEX-mode

I have some text(?) files that since version 4.5.6 always opens in HEX-mode. They opens and looks fine in notepad and other text editors, and was always treated as text in PSPad before I upgraded to 4.5.6.

Is there a way I can force PSPad to open files as text?

PSPad has reason if he open file in HEX mode. I guess your file contains some nonprinted chars from the begin of ASCII table.
You can switch off binnary file detection.
Go to Program settings / Direct edit button
Change variable of: AutodetectBinnary=0

It was a handful of white spaces at the start of the file.

Changing the setting solved my problem, thanks a lot.

Can I comment out lines in "Direct edit"?
(I like to keep a copy of the original values, both to remember what I have edited manually and the default value.)

You can. But you can delete line - this will reset setting to it's original value.