Section 19(5)(b) of the legislation that underpins the Scheme - the Mother and Baby Institutions Payment Scheme Act 2023 - provides that an applicant to the Scheme shall specify what benefits they are applying for. So, applicants can indeed select just the medical benefits and not the general or work payments. (In practice, the Payment Scheme Office will assess every application and where it finds that an applicant may be entitled to more benefits than applied for, will engage with the applicant to double check their selection.)
An applicant who chooses only to accept health benefits under the Scheme (either the enhanced medical card or the health support payment) does not waive any right of action or does not have to discontinue any other instituted proceedings.
However, I would just highlight that Section 19(4) of the Act is also relevant here. This section precludes more than one application per person unless in one specified circumstance. Essentially if an applicant does decide to apply for health supports only, there is no opportunity to submit another application for a payment at a later date.