Cold setting isn't something super technical. Essentially they just yank the dropouts out a bit, then use a Frame/Fork Alignment tool to make sure the dropouts are parallel after yanking. If they aren't they use the Alignment tool to kind of bend things around until its as close as they can get. I guarantee you that any shop that tells you they have experience doing this does NOT have the right tools. The correct and appropriate tool uses to be known as a frame spreader. Like the Hozan C-451. People don't realize how unqualified the average LBS is at working on bicycles. Essentially most are staffed by young kid "mechanics" that know less about bicycles that most of us here on the forum. After the shop tells you they have the right tools, have them show you the tool. It should look something like this:
http://www.hozan.co.jp/cycle_e/catalog/C451.html
Or a Park Frame & Fork Straightener if they don't have the correct chain stay tool:
http://www.parktool.com/product/fram...ightener-FFS-2
There should absolutely be a specific tool that they will use, and not just some homemade tool like and axle with some washers:
If you don't mind my asking, why bother? You can easily slip a 130mm hub into a 126mm bike. For crying out loud we Cannondale cyclists do it constantly, and we can't spread anything or the bikes would crack. It takes a second longer when inserting or removing the hub, as you have to gently pull the rear stays apart.
However, the much more elegant solution is to take whatever 130mm hub you want to use, I assume a cassette free hub and actually look at the thing. I've posted this before, and
most people don't know this trick, but looking at the Ultegra 6500 Hub here next to my computer there is a spacer on each side of the hub. In between the outer locknut and the cone. You remove the spacer on each side and if you don't have a hub that measures 126mm its imperceptibly close. You do NOT need those spacers. Take them out and its a 126mm hub. Look at the front hub of any subset. Its outer locknut up against the cone on the Ultegra 6500 matching front hub. Your local bike shop will never tell you this trick because they want to sell you a new hub. But its common knowledge.
I'd make the hub you want to use 126mm if you can, before I'd start bending my frame on purpose, but that's just me. Besides if you want to use a freewheel you can't get a better hub than a Mavic or a Phil Wood. The Mavic has a slightly smaller axle where it necks down through the bearing. However, most people don't know that Mavic axles have 15mm axles that neck down to 12mm at the bearings. For the record Phil Wood axles are 15mm which is why they are so great for touring and tandems. You'll never have a problem breaking an axle on a Phil Wood using a freewheel. I'm heavier than most tandem teams and my Phil Wood hubs have never complained. Mavic hubs are absolutely the equivalent of anything ever made. Sealed bearings, spin forever. You can easily find Mavic 126mm rear hubs and throw a new IRD Classica freewheel on it. You can't find a higher quality AND better shifting freewheel, its never been made. IRD had nightmare problems with previous generation freewheels with the pawls failing essentially immediately. Avoid anything previous gen, and ensure its a Classica.
If you don't like just taking a sec to finagle a 130mm hub into your dropouts, and you don't want to remove the spacers from your hub or it doesn't have any then for the price of paying a teenager to spread your dropouts you can buy the actual tool yourself:
IceToolz E263 can be had for $65 + $5 shipping on Amazon.
You're welcome.
Its not a shop quality tool, but if you go slow you can have the pride of doing it yourself. Or you could ruin your frame set, if you really didn't know what you were doing and buggered it. Using frame tools on a bike frame is use at your own risk. Spreading the chain stays is actually the simplest and safest as long as its steel. When you get into the weird and impossible to find tools for straightening head tubes or just trying to fix a seat stay or fork, bad things can happen instantaneously.