Short answer. Yes, but only as a rebuttable presumption. Rule 131, Section 3 lists among the law's disputable presumptions "that a person acting in a public office was regularly appointed or elected to it." Like all the presumptions in that list, it holds only if uncontradicted and can be overcome by other evidence.
What the law says
The following presumptions are satisfactory if uncontradicted, but may be contradicted and overcome by other evidence
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
What the law says
That a person acting in a public office was regularly appointed or elected to it
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
What the law says
That official duty has been regularly performed
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
The general framing: disputable presumptions
Rule 131, Section 3 opens by describing an entire category of legal presumptions and how they work: "The following presumptions are satisfactory if uncontradicted, but may be contradicted and overcome by other evidence." Everything that follows in this section, including the presumption about public officers, operates under that same qualification — it stands unless someone actually contradicts it with evidence.
The specific presumption for someone acting in public office
Among the many presumptions the section lists is this one: "That a person acting in a public office was regularly appointed or elected to it." So yes — if someone is actually acting in a government position, the law's default assumption is that they got there through the proper appointment or election process, without requiring that assumption to be separately proven every time the question comes up.
A related presumption for how the office is used
The list continues immediately with a closely related presumption: "That official duty has been regularly performed." Where the presumption about appointment covers how someone got into the position, this one covers how they carry it out — the law presumes, again unless contradicted, that whatever official acts they perform in that office are performed regularly, rather than requiring proof of regularity for every act. Together, the two presumptions cover both ends of a public officer's standing: how the office was obtained, and how it is being exercised.
What 'disputable' means for this presumption
Calling this a disputable presumption is the whole point — it is not the same as a conclusive fact nobody can challenge. Anyone who has actual evidence that a particular person was not properly appointed or elected to a public office can present that evidence to overcome the presumption. Until that happens, though, the law does not make you prove regular appointment from scratch every time someone's status in a government position becomes relevant. The presumption applies only to the fact of appointment or election itself, not to whether the underlying qualifications for the office were also met.