Any "agreement" would start and end with the "Be worth checking all this as it may be different for otm drivers. I don't work for colas" bit tbh. However, you're welcome for that all the same.
If you know* something, great, pass it on. If not, it's better not to waste people's time misinforming them with hearsay. For example, the pay deal you say is "agreed" was implemented, including back pay, in November. But that's for freight drivers, not the plant side, who have totally different salary, terms and conditions, and it's therefore utterly irrelevant here. Your guess about rest day pattern bears no resemblance to reality, none at all. I've been driving trains for Colas for nine years, and yet I didn't try to provide any info here, because I don't have the first clue about the plant side of the company, and LeGrimpeur clearly stated the job he was interested in was driving on track machinery. It would help nobody if I had a wild stab in the dark, so I don't.
You're not the first person I've seen (or pulled up, for that matter) posting guesswork about Colas, and I'm bewildered as to what the motivation of people who do this is - there's an awful lot of companies in the railway industry, I've no reason to suspect each one won't have several people with no connection to the company passing on utter bunkum in places such as this - that they probably don't realise isn't true - to people who come here in good faith for a bit of information. This is not just a dig at you personally, this section of the site is riddled with people guessing (sometimes very wildly, sometimes making statements about companies I've never worked for yet still know to be 100% wham) at something and imparting it as if they are some sort of authority. It annoys me, because taking advice (thinking it to be legit, which is turned out it was not) from someone doing that cost me a job in early 2013. Luckily, I ended up in a much better job by the end of that year, but others won't be so lucky, and it isn't right to mess with people's lives like that, nor to waste their time.
Have a happy new year.
* As in know it to be a fact, not think it to be a fact.