You will need a cable and housing cutter. You would need to remove the cable from the housing and trim the housing to the desired length. After the housing is the length you desire, making sure it is not too short for safety concerns, thread the cable thru the housing and reconnect to the pinch bolt assembly of the component it operates and realign for proper brake and shift adjustment. * N.B. after cutting the housing an awl or like tool should be used to open the end of the housing to reduce the friction to the cable feeding thru the housing.
It is easy, but will require proper tools and knowledge of bicycle alignment.

I was hoping to be able to trim the housing with the cable inside, much like you do with electrical wire and housing (score the housing and pull it off without damaging the underlying cable). Is this wishful thinking?

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Thanks to Euro-Sports for my H3Cs.

http://www.euro-sports.ca

Wishful.
I don't think it can be done that way. If it can you will make history.

Tks a lot for the replies.....sounds doable with the proper tools.

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Thanks to Euro-Sports for my H3Cs.

http://www.euro-sports.ca

Housing/Cable cutters work fine on shift+brake cables and shift housing. I think they work mediocre on brake housing. (due to steel lining) I will use a dremel tool with a cut-off wheel and trim the housing. That leaves a perfect cut with almost no need to "fix" the housing with an awl.

No dremel tool. Sounds good re using cable/housing cutters on the parts you mentioned. If brake cables are metal lined I could prob just use a hacksaw and zip through them in a few seconds.

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Thanks to Euro-Sports for my H3Cs.

http://www.euro-sports.ca

Gee, if you're going to go that route, you might as well go big and use a table saw!

Good housing cutters and a nail do a great job - tried, tested and true. You don't need to be exact with brake cables - once the ferrule is on tight, they hardly compress at all.