USyd states that Dalyell Scholars are expected to maintain a cross-semester average mark (CSAM) of at least 75 for every full-time year that they study (or equivalent). A student's CSAM is determined using the following formula:
Essentially, a CSAM is the WAM that a student achieves across all units attempted in a CSAM period, which includes all semesters required to complete at least 48 credit points (i.e. typically 8 units). If this minimum requirement is not met, the student may be removed from the Dalyell stream, although Dalyell units that they have completed will still count towards meeting their degree requirements (where applicable) and their enrolment in their course will not be at risk.
The reason that I am discussing this is that USyd appears to emphasise and prioritise the requirement of reaching and maintaining a minimum academic standard in order to remain in the Dalyell stream, as opposed to whether a Dalyell Scholar studying their degree full-time is compulsory. This brings us back to the aforementioned statement, specifically the "or equivalent" part, from which one can infer that a Dalyell Scholar has the option to study their degree either full-time or part-time and that meeting the minimum academic standard requirement is what USyd actually cares about.
It would therefore be reasonable to suggest that you can safely take on your position (of course, it would be a good idea to contact USyd to confirm this just to be safe). Keep in mind that a full-time study load consists of taking a minimum of 18 credit points (that is, 3 units) per semester (anything below this is considered a part-time study load), meaning that you may not necessarily be classified as undertaking a part-time study load even if you do not take 4 units each semester.
I hope this helps!