How to set default file format for MS Paint [duplicate]

I'm using MS Paint on WinXP at work, for capturing simple screenshots.
Problem: MS Paint always wants to save in BMP format.
How can I set PNG to be Paint's default file-saving format?

Note: Suggestions about other software are irrelevant. I know there are many other software tools available. But I'm asking specifically about MS Paint.

I'm afraid this is not possible, based on this answer to a related question. It would be good if someone can confirm this.

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