Need clarification regarding credit card

No you can't

no, it doesn't work like that.
btw if u want i can help with my hdfc cc.
DM.

If applicable, use 8K gift vouchers and pay the balance within your credit limit.

U can do that in one card I think but u need to pay overlimit panalty

Yes. I have done such in the past. Search here, you will find many done that

Disable the Overlimit, and then try to do that transaction.

Call up cc and ask for advise... If your card usage and payments are good some banks give temporary limit increase for a specific period

Risk !!!

Using 30% itself is Bad,

U want to use more than 100% that too in a single transaction.

Yes I did this exactly,

I bought a laptop worth 1 lakh 10 thousand with my icici credit card of limit 90000.

I prepaid 30000 to my credit card, It showed -30000 as limit.

I then ordered the laptop, got the offer within limits.

Just remember to prepay again and reduce the usage to less than 30% before bill is generated.

ICICI worked, can't 100% confirm for HDFC but might work.

You can do that. Did it with my SBI CC.

There will be a transaction limit set by you for each category. How come that can be more than your limits?

i think it may reject stating that purchase limit exceeded. so a single purchase would have that issue

Change the limit to 0 in the App and then add funds 

almost works for all cc