reg. import of tiff images

Hi,

I created a location and map set for my project work. I have given
the easting, northing and resolution etc. My land use, soil and
elevation information are in tiff format (without world file) Can I
import the tiff files straight away using r.in.tiff followed by
r.support.

If world file is a must where and how can i create a world file?

One more question

How can change the category value for a single cell or a few cells?

Suggesstions are requested

Please reply to yourkannan@hotmail.com or to this e-mail address

Department of Engineering Hydrology,
Powder Store, Nuns Island,
National University of Ireland-Galway,
CO GALWAY,
IRELAND