It is clarified by Income tax department (via Circular no. 4 dated Apr 5, 2023) that employee can choose either old tax or new tax regime for the purpose of TDS deduction on his salary and employer should follow accordingly. In case employee does not intimate his choice, employer shall follow New tax regime for TDS calculation.
New tax regime for FY 2023-24 is beneficial for all salaried people whose income does not cross Rs. 7.5 lakh and they may choose new regime straightway. For others having income >7.5 lakh, they need to choose carefully (considering exemptions available/investments they are going to make during current financial year) so that their take home does not get affected.
Is this choice made at beginning of FY final?
No. One can change option at the time of ITR filing. There can be circumstances a) where one might have got increment or promotion or changed jobs resulting in higher income, b) where one might have left the job during the year etc. So your tax consultant should be able to make right choice at the time of ITR filing.