The easiest way to do this, and probably the most popular method used by people here, is to print out the tiles on sticker paper and cut them out and stick them on to existing tiles (ones you have doubles of or don't plan to use). This is a very effective method. Nearly impossible to detect just by feel.
That's the technique I'm using to make custom tiles. I actually bought a cheap base set on eBay to re-use. Cost about €5 including shipping. And I still have a misprinted copy of the Wheel tiles left, which were replaced by HiG. (Thanks for the great service
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