ILR achieving the salary threshold

I am on Tier 2 general and will qualify for ILR in March 2018 and I understand that there is a salary threshold of £35,000 until 6 April 2018 (after which it becomes £35,500 for a year). Now,

1) If I ask my employer to increase the salary instead of giving the annual Christmas bonus would this be ok? This way, all the employees will get bonus but I will have increased salary instead.

2) Am I allowed to work for more no. of weekly hours than what was written in my CoS, and have this total income counted towards salary and not as over-time? If no, and if I decide to do that what is the procedure? Also, if I specify more no. of hours in my extension application (due in March 2016), would there be a problem?

3) Currently my salary stands at £31,000. Is my employer having any prohibitions under labour law to increase my salary in one or two steps so that I meet the threshold? I hope there are none, otherwise this seems like a an impossible criterion.

Thanks for any advice!