The source of my confusion is which mods are for which models.
Can any body advice me as to which modifications are suited to my model.
But what about the CO2 adjusting up 10 points etc is that applicable to my model?
You cannot adjust the CO on the XTZ unless you buy one of these. It doesn't make a whole lot of difference on the Tenere either as the surging was/is not so much of an issue as it is on the R/X models.
And tires how many times have i read that forum. Which tires are for me no idea. 80 percent on road (work) about 140 km everyday and a little mud and mainly forest tracks on the weekend. Other things to consider is i ride in the rainy season with heavy panniers (work).
Tyres are a matter of personal taste - you'll end up with a million-and-one different answers (as you've already found!) 
Due to heavy panniers considering getting wider tyres, upgrade chain and sprockets but which tyre?
You can only really fit a 140 on the back as an alternative, and that won't make much difference although it does have a slightly higher load rating. You can get 525 chain and sprocket set to replace the standard 520 from here. Most find the standard tyre/chain combination fine when loaded up though?
Considering tkc80 or tourance ex or (avon distanzia (maybe not this because too difficult to change)(no close bike shop)) i like the sound of tkc80 as many people say there easy to change, can handle light of roading
and have good mileage. Worried about the long road work and heavy rain.
A TKC80 is a great tyre on the XTZ, but it will most definitely NOT give you good mileage!!
As i understand many people are exchanging their front sproket to 14 tooth to increase low gear power. After some research it is adviced elsewhere not to decrease the front sprocket as this increases ware to expensive parts but to increase th rear sprocet by two to four teeth. Is this advisable?
Going up by three teeth on the back will lower the final drive ration by the same as a 14T front and will save on sprocket wear too. However, you will need to buy a longer chain which cancels out any money saving.
Also with regards to the rectifier would it be safe to assume that if after 29000 km on the clock without trouble then i the part is not faulty?
Most (but not all) reg/rec issues were on 08 bikes. You may well be OK by now, but it is always worth checking the connector is seated correctly and use some dielectric grease to help seal it from the rain (especially in your climate!)
Finally is anyone making and selling any long lasting cush dives? It seems like a easy way to make a few quid for the right person.
I've thought about it and made some enquiries, but can't find a company in the UK who is prepared to do it (yet).