Return u/s 44ad

Yes, it can be filed for AY. 2018-19; As per amended section, effective from 01.04.2017:::

Consequences if a person opts out from the presumptive taxation scheme of section 44AD

If a person opts for presumptive taxation scheme then he is also require to follow the same scheme for next 5 years. If he failed to do so, then presumptive taxation scheme will not be available for him for next 5 years. [For example, an assessee claims to be taxed on presumptive basis under Section 44AD for AY 2017-18. For AY 2018-19 and 2019-20 and he offers income on basis of presumptive taxation scheme. However, for AY 2020-21, he did not opt for presumptive taxation Scheme. In this case, he will not be eligible to claim benefit of presumptive taxation scheme for next five AYs, i.e. from AY 2021-22 to 2025-26.]

Further, he is required to keep and maintain books of account and he is also liable for tax audit as per section 44AB from the AY in which he opts out from the presumptive taxation scheme. [If his total income exceeds maximum amount not chargeable to tax]