The First Scotrail liveried 156s aren't expected to be reliveried for some time. They've just received a refresh and will be in FSR livery for some time. All the West Highland Line trains are First Scotrail (ie, not SPT) units; they have been fitted with the equipment for
RETB signalling. So, don't expect the reliveried trains on the WHL for some time.
Re: Airdrie-Bathgate, there is a timeline
here which I hope will be of use. Drumgelloch will close temporarily for relocation in Spring 2010. In Summer 2010, works will begin on the Airdrie station upgrade, which basically seems to involve an upgrade to 3 platforms (reopening the platform opposite P2) and a renovation for the station, although the existing ticket office and shelter will remain.
Looking at the
plans, it appears as though the single track section on approach to Airdrie will need to be doubled. This will require a closure of Airdrie station, although probably only for a week or so. They'll need to replace a good bit of the track on the run onto Airdrie station, which will need to allow for trains to through Airdrie all the way to Edinburgh, but also into P1 and the siding as they do just now. The closure will be in the Summer, so probably won't affect your school commute. If they have any sense, they'll do it during the Glasgow Fair (ie, this time next year) to minimise impact.
This all assumes that they do not need to reconstruct the bridge at Craig Street to accommodate the two tracks. I've not visited the station for a while so I don't know if you'll be able to fit them in.
I presume they'll terminate trains short at Coatbridge Sunnyside and bus people to there whilst the line is closed, but I cannot yet find a definitive plan. At the moment, there are no advertised closures on the North Clyde Line in relation to this project.