For cameras, helmets, steering wheel positions , use TeamEditor.
For Tyre positions, check the settings of the cars which are diffrents with teameditor ( have a look with the v cam), adjust the settings, write the settings of these tyres positions. re-adjust the default tyres positions (Don't forget to click on the "apply" button before to quit)
Then, copy and past the GP4Tweaker files into your main GP4 folder (look at the readme file for installation infos). Edit the tyrepos.ini fils into the gp4tweak_data folder with the settings for the tyres you want to modify.Finally, edit the gp4tweak.ini file and set tyrepos.ini on 1, save.
It's done.
____________________________________________________________________________________________________________________________________________