I8AHSV: it is possible to reset a spring by heating it. Theres a few companies that heat the spring fully, straighten it out, and then load it up into a shorter spring. Tis is the same method they use to create the original spring, so the workshops you have talked to should take a long hard look at themself, and decide wether they should still be in the suspension business.
But yes a lot of them do chop the spring to make it lower. In the falcon this is safe as its a coil over shock design, so the coil isnt going to pop out of place when you go over a bump. In a commodore the rear suspension is different, where the chock just sits in there, if its chopped, and the shock isnt matched to it, its quite possible for the coil to pop out when you are driving over a bump. The holdens coil btw isnt even bolted in. its slotted in, and sits there, oh the quality.
but chubbz, i would say go KYB if your on a budget, they are pretty stiff, and are well priced, i have them in my car. But if you have money, go for koni adjustables, and set them to be stiffer.
BTW, dont lower the car anymore, it'll just look stupid, and be hard to drive around. and it will also make your car handle worse being so low.