For the 4g15 from Auto to Manual is pretty easy. You need one Manual gearbox, new clutch parts preferably, clutch master cylinder and slave cylinder, clutch pedal kit, gear lever (doesn't usually come with the potong gearbox) and that's pretty much it. You will need some small components here and there but nothing too difficult. However, I am not sure if the driveshafts on the auto box are similar to the ones on the manual box so do look into this.
Chances are you may not need to cut a hole to mount the clutch pedal and master cylinder because most manufacturers use the same body for an auto and manual and these parts on an auto car are just usually blanked off. Worse case scenario is you'll have to cut but the markings are already there.
As for the manual to auto one. Well, depends what car you're driving really. Some cars gather information from the Auto box and may not share the same ECU as a manual car. If you drive an ancient car then you gotta think about vacuums and all that but this is really slim. The ECU is the biggest problem I see but then you can always replace your ECU and do a bit of DIY wiring to accomodate. :D
Oh and for either case, chances are you're gonna need a recalibrated speedometer to go with your conversion.