ecscI haven't re-read the scheme booklet, so just going from the...

ecsc

I haven't re-read the scheme booklet, so just going from the wording in your quote:
"For the Merger to proceed, the Scheme Resolution must be approved by a majority in number of Biota Shareholders present and voting at the Scheme Meeting (in person, by attorney, by proxy or, in the case of corporations, by corporate representative) (unless the Court orders otherwise) and at least 75% of the total number of Biota Shares voted at the Scheme Meeting"

This would entail:
1/. "... approved by a majority in number of BTA shareholders present and voting"
(so each shareholder regardless of shareholding carries 1 vote. At least 50.1%, or a simple majority by headcount, must support the merger); and

2/. "...and at least 75% of the total number of Biota shares voted.."
(which implies that the weight of your holding is important. All the shares voted [not total share capital issued by the company] are counted and the % of shares voting FOR the merger must be 75% or more of the total number of shares casting a vote).

Hope that is clearer than mud.

With regard to cancelling your current vote lodged, you can access your Biota shareholding in LINK, amend and resubmit if that is your wish.