Could a country get their preferred candidates to win an Australian election by declaring all other candidates for that office citizens of that country, thereby making all those other candidates ineligible for the office? Can they get a current office-holder to be dismissed from the post by declaring them a citizen?
At the risk of stating the obvious: This would be considered an act of aggression against Australia as a nation, not merely against one political party.
Let's suppose the UK is having trouble negotiating a post-Brexit trade agreement with Australia. It suddenly grants UK citizenship to the Australian Prime Minister and Cabinet. This means they are dismissed from office and the UK can now negotiate with a different Prime Minister, right?
In any practical sense, no. This would be considered unacceptable interference in Australia's internal politics. Most likely, whatever Australian government remained in office would push through emergency legislation to nullify this British mischief-making. The principal effect would be to permanently damage relations between Australia and the UK.
(The UK is just an example, much the same would apply to any other country.)
From an opinion piece published by the public broadcaster Australian Broadcasting Corporation What the High Court citizenship decision says about the health of our democracy
The standard is a strict one: It is no excuse, for the purposes of section 44, that an MP has no real ties to a foreign power, or did not in fact know they were a citizen of another country.
But it is not a wholly absolute one: the court recognises foreign countries cannot make it impossible, or unreasonably onerous, to renounce allegiance to that country. To allow this, the court held, would impermissibly undermine "the constitutional imperative that an[y] Australian citizen" be able to participate in representative government.
If a foreign government was trying to deny an Australian citizen being able to be a MP, let alone try to get a particular candidate elected, that would likely not be in contravention of section 44 of the constitution.