Short answer. Possibly, yes. Rule 132, Section 21 excuses a private document over thirty years old from separate proof of authenticity only if it is produced from natural custody and is unblemished by any alterations or circumstances of suspicion. Handwritten corrections can count as alterations, so they may take the document outside this exception.
What the law says
Where a private document is more than thirty years old, is produced from a custody in which it would naturally be found if genuine, and is unblemished by any alterations or circumstances of suspicion, no other evidence of its authenticity need be given.
Rule 132, Section 21 — When evidence of authenticity of private document not necessary. Read the full provision →
The three conditions the rule requires
Rule 132, Section 21 lets a private document skip separate proof of authenticity, but only where three conditions are all met together. The document must be more than thirty years old; it must be produced from a custody in which it would naturally be found if genuine; and it must be unblemished by any alterations or circumstances of suspicion. All three have to hold at once — age alone, or age plus the right custody, is not enough if the third condition is not also satisfied.
Why 'unblemished by any alterations' matters here
That third requirement is the one your handwritten corrections put in play. The rule's own language, unblemished by any alterations, is written broadly, and a handwritten correction is, on its face, exactly the kind of change to the original document the phrase is describing. Because the rule requires the absence of alterations rather than merely the absence of serious ones, a document carrying visible corrections does not automatically clear this condition the way an untouched document would.
Not every alteration necessarily defeats the exception
The article does not define what counts as a disqualifying alteration versus something that does not defeat the exception, and it does not say every mark or correction, however minor or explainable, is fatal. What it does say is that the document must be free of alterations or circumstances of suspicion, so whether specific handwritten corrections on your document are serious enough to be treated as the kind of blemish the rule has in mind is a factual question the bare text alone does not resolve.
What happens if the exception doesn't apply
If the corrections do take your document outside this exception, that does not mean the document becomes unusable — it simply means the ancient-document rule in Section 21 will not excuse you from otherwise proving its authenticity. You would then need to establish authenticity through the ordinary means the Rules of Court provide for private documents, rather than relying on age and custody alone to skip that step.