Tier-2 extension with new employer-- URGENT

I have been on my current company in shortage occupation (planning engineer ) for 4 years and my visa expires on 21st march. i have been offered a new position as a software developer in normal SOC code category and date of issue on COS is feb13 2017 and the employment start date is 1st march2017. please respond to my doubt sand concerns below

1) can i switch from shortage occupation list to new SOC (2136- this is considered as both normal and shortage occupation) but i will be applying as a normal SOC . will the case officer ask any questions if i go for premium service about my change of profession from planning engineer to developer.

2) as the start date on my COS is 1st march ,how long before the start date can i apply for extension online and if i get an appointment for premium after the start date what can i do?

3)my current employer will allow me to work until my present visa expires on 21st march , but how long can i work with current employer( is it until when i fill online application or the start date on COS or until i get my new visa)

please help me with these questions
thanks

Some points to consider
You can not move to a new SOC outside of the current shortage occupations without a RLMT being completed. So if that has not been undertaken then the job can not be offered to you. Was there a RLMT undertaken? I have assumed you are staying with the same employer?

If all is ok with the above and you can proceed then the next point.
You can continue to work for your employer in your current role pending the outcome of your extension application. Once your visa is granted you can move roles.Your employer can carry on employing you under the current role without the need to stop working as long as you continue with your current role.

Will your change of role cause more scrutiny of your visa application - Yes because of the requirement for a RLMT. There is nothing preventing change of roles but it does get you noticed.

Thanks for ur answer Frontier Mole,

i am moving to a new employer and the RLMT has been undertaken and the required salary has also been met.

when u said it would cause more scrutiny of my visa application, will the case officer consider any other points other than RLMT , required salary been met and the sponsors rating?

The guidance states that as long as everything is met in the way of RLMT and salary it should all be ok. This assumes all the other areas are met.
What can cause complications is the change of SOC raises the question of the transferability of your skill set and potentially the genuine vacancy concern. Closely aligned roles may not be an issue but jumps across business sectors and nominal skill sets do.

Thanks a lot frontier mole,

I am moving from planning engineer to programme developer, I am hoping that it wouldn't cause any complications and the employer is genuine too as they have carried out proper RLMT.

could u also please help mw with other questions I have asked

1)can my sponsor (new employee) change the start date on COS or do they have to issue new one. the reason for that is I have only 7 days before which I have to apply my visa(before start date of job). I can do that but I have some issues so I need more time.
2)do I have to definitely apply for before start date??

1. they can add a note to reflect the change of start date on the current cos, or issue a new cos by paying the 200 again to have the new start date.
2 u dont have to apply before the start date

Thanks iworker for your reply... apprecaite it