Can the width of Ikea Ivar shelf boards be shortened?

Hello,
Our apartment is full of Ivar shelves - with cabinets, large, small, with wardrobe, with glass, painted, with clothes rail, etc.

But now we have a problem:
We just bought an old school. Our (beloved) architect made a faux pas.
He was supposed to install 3 niches in the hallway, into which the bookcases (Ivar) should fit, two next to each other each.
He already planned it - but unfortunately as rough construction dimensions. Now I'm sitting here and have no shelves that fit there.

Is there a trick to shorten the Ivar boards in width? Has anyone had experience with that??
Unfortunately, Ikea - unlike, for example, Lundia - only offers the 40 cm width now, which doesn’t work for me.

Can you remount the slats if you remove them from one side??? Does that hold?

Thanks

Hello,

I did this after our last move; shortened from 40 cm to about 37 cm.
With the boards - bought in 2009 - that was no problem.
Carefully break off the narrow strip of wood above the metal strip. Then pull out the rail.

Straighten the small curved metal hooks that held the rail.

Draw the contours for the new length precisely and saw them out, cut the long slot into the end face.
Compare with the original and, if necessary, rework, then press the rail back in.
Press the small metal hooks into the wood for securing - done.

I did this with a fine saw. The long slot was first cut with the fine saw and then brought to the correct width with a hacksaw that has slightly coarser teeth. The slot must be able to accommodate the rail without resistance. Otherwise, there is a risk of breaking!

This took longer than this answer here, but there is no visible difference from the original and it holds.

Regards

Lutz