Is there any trick to give extra working time with gumpaste if you need to make a detailed piece?
I know shortening...but will gumtex give it more time, or any other such things? And then will it still dry hard as a rock?
Depending on what your making, you might want to go with fondant and tylose powder instead. It will give you more time. The other option is if your making your own gumpaste you can always add less tylose which gives it the drying quality which would give you more time. But it all has the problem of drying out and getting elephant skin at some point.
I agree with weirkd. Fondant plus tylose is a good way to add work time without compromising strength. If it's too soft at first, just let it rest for a few hours until it's more like the consistency of gumpaste.
You can also mix a bit of fondant in with your gumpaste. Depending on what you're making, 75/25 gp to fondant is a good ratio. More work time, dries hard.