Will it void warranty!? [Opening laptop]

Hello.

I bought dell inspiron 3558  from serbian official retailer in september last year as i remember.
And now i have to..idk,extend that warranty by 5 years which dell gives in cooperation with "Nepo System".

Now the problem is,thats quite a long lasting procedure since i need to ship them laptop once every year to get them to regulary check it so i can still have warranty on it.

The question is:Can i open laptop,replace thermal paste on cpu and gpu because im preety sure that they arent the best and i would like to apply quality thermal paste on it?

Will opening and replacing thermalpaste(removing heatskins and stuff) void my warranty?

Thank you.

one more question guys:

hdd is making some strange noise...its not loud or anything,but when its quite i can hear cracking noise from it when its working,is this normal?