bulgie 

The amount the fork shortens as you add rake depends on where on the blade you add it. If you add curvature at a small radius down low near the dropout, that gives the maximum amount of shortening. That can be helpful if the fork is too tall and you want to decrease the clearance over the tire.

More often though we want the opposite, more rake without lowering the fork too much. To do that, add rake (offset) as high up on the blade as possible. The ultimate is bending the blades forward right where they join to the crown, which results in almost zero decrease in the fork height. The amount of bend needed up at the crown is very slight; generally will not make the fork look crashed.

If bending the blades forward at the crown doesn't appeal to you, there is a middle path, which is to add curvature but with a longer radius, and add it near the top of the current rake curve. Being higher up, this results in less shortening of the fork. Not zero but usually an amount that can be tolerated, unless the fork was already borderline too short.

Whichever way is chosen, doing it precisely, to get exactly the wanted amount of increased offset, requires an operator who knows what they're doing. It can theoretically be done with just a vise, but it's best to do it in a dedicated fork alignment fixture and/or raking form, that generally speaking only framebuilders (FBs for short) have. And maybe only older FBs at that — "kids these days" often just put carbon forks in their frames, and may not even have the equipment for making or aligning steel forks. You may or may not have a FB near you who offers that service, but if you're willing to ship the fork then you have more options. Consider talking to BF's own gugie who has a proven track record in this very kind of thing. (I don't know if he likes getting forks sent to him for mods, talk to him about that..)

I hope to be able to offer that kind of service soon. I just finished my fork alignment table and it's a beaut, a hundred pounds of cast iron, very stout! See it here: https://flic.kr/s/aHBqjzU3gW
Next I will build the raking form (bender) that lets me add offset by increasing the curvature. My capability to do that, so far, is pretty rudimentary: a wood form repurposed from a round bar stool seat. But I plan to build a stronger one, probably out of steel, hopefully by the end of June (stay tuned!)

Mark B in Seattle