You can have most cheek pieces altered to be adjustable, Small bore prone rifles are modified all the time for adjustable cheeks. Last one I had done was by Gunsmithing inc in Colorado springs, now closed but many other people do the same job.

Basically all they do is band saw the stock then insert the adjustable mechanism.  Usually with adjustable butt plate, as you alter the cheek height the butt plate generally needs to be moved too, I don't have photos on photo bucket so can't post but if you PM you Email address to me can send you some pictures. I just sold a prone rifle and still have the photos.

I don't know the particular rule you will be shooting under but many matches don't allow adjustable cheek pieces. Small Bore and high power match rifle does.  Check first

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