It's required for nri students only as per the 2019 neet karnataka

Yes you can submit new one

Yes it is mandatory to submit the same 

Yes you can submit the new income tax certificate 

Those claiming reservation benefits: Caste / Caste Income Certificate issued by Concerned
Tahsildar- For SC / ST in Form-D, Category-I in form E and 2A, 2B, 3A and 3B in Form F.
1.2 Clause b

2) for others income tax return certificate is not necessary for NEET medical verification 

You can submit fresh income certificate 

Income certificate is valid for one year. years old certificate is invalid. Recent financial year certificate will submit.

If you are claiming any reservation then you have to provide the income certificate issued by the tahsildar and it's not be very old it is mandatory to provide your income certificate issued by Tehsildar to claim any reservation based on the economic background

Dear Sir,

You can do that. First read the instructions between the lines. IT returns and Certificate issued by Tahasildar has different meanings and weight ages.

submit fresh income certificate 

If you belong to any category or have applied to a scholarship then submitting income tax return certificate becomes a necessity, however if its not the case then its requirement is not needed so you should first enquire in the college before submitting any such important proof document..

The income certificate issued b the revenue department/Tahsildar is valid for one year only, hence you may have to obtain a fresh income certificate .

1. Yes Income certificate is necessary for admission in Karnataka through neet. 
2. It should be issued by concerned Tahsildar.
3. It should be of the current year.