Can't retrofit parameters of Helix

[Mazata]

Hi,
Once I've defined a Helix and pressed "ok" in the dialog box, is there any way to go back to that dialog box in order to edit the defining parameters such as revolutions, resolution etc.? Since the resulting Helix appears as a sketch object and not a helix object, all I'm able to do is to get to the sketch editing menu, but not the helix-editing one.
I've tried setting these parameters equal to some previously defined UserParamter, but the helix won't update once I modify the values of my UserParameter. Any idea what I'm missing?
Cheers,

Theo