Can pixelation be reversed?

No — each block replaces its pixels with their average, permanently discarding the detail. That's what makes it real redaction, unlike a light blur.

Can I pixelate just part of the image?

Yes — whole image, a center block, or a horizontal band across the middle.

No — and for real privacy, also strip the EXIF metadata with the Photo Metadata tool.

Mosaic an entire image or just a region for quick redaction of faces, plates and screenshots — pixelation permanently discards detail.