I might advise the more conservative approach on this one since the additional money is not part of the RMT and they are separate transactions.
From the OSC: 23(a)(1)(3)
When a consumer buys or builds a new dwelling that will become the consumer's principal dwelling within one year or upon completion of construction, the new dwelling is considered the principal dwelling if it secures the acquisition or construction loan.
and 23(f)
3. Combined-purpose transaction. A loan to acquire a principal dwelling and make improvements to that dwelling is exempt if treated as one transaction. If, on the other hand, the loan for the acquisition of the principal dwelling and the subsequent advances for improvements are treated as more than one transaction, then only the transaction that finances the acquisition of that dwelling is exempt.
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The opinions expressed are mine and they are not to be taken as legal advice.