Anyone had the equipment customized ?

Yes; kinda, maybe, sort of.   Being a electrical design engineer, I design a log of amplifiers and analog control electronics at work.  So naturally, I do this at home with some of my equipment.  For a while, I was doing custom electronic design for folks who had high end stereos. 

The key is finding where the weak spots are in the equipment, then making those spots more robust.   By weak spots, I mean where the designer left performance on the table and didn't pack it into the product.   Anyone can tweak stuff, which may or may not sound better, and may not give you much bang for your buck.   And, trust me, hiring someone to do custom engineering on your equipment is expensive. 

If you go this route, pick someone who routinely modifies your brand and model often.   That is, they have a long history of fixing that particular model.   Ideally, they should be someone who actually worked at the factory or someone who worked in their service dept.  If they don't meet this criteria, don't send them your equipment or money!

It’s interesting. I don’t really hear of customization spoken about much.

Restoration is returning gear to original condition using the same brand and value of parts as the original.

 Upgrading is changing the manufacturer of the parts that are being replaced to increase reliability or out of convenience, but keeping the values the same and not altering the original circuit.

Modifying is changing the parts as well as the values and circuit design. 

We see all three in the land of vintage electronics, and I have done all three, as needed. 

I think of customization as adding inputs, changing the gain to suit a particular source and output, maybe painting or chromeing some parts, stuff like that.

I have had Steve McCormack mod and upgrade his equipment, which I would consider 'customising', as I can pick and choose what I want done.

B