I did once, but in different format and in Canada

After mortgage was pre-approved, I got my HELOC increased for downpayment. But this must be cooperated by the first loan manager, as he/she needed to know where your downpayment come from. If he knew your downpayment came from HELOC, he supposedly recalculated GDSR/TDSR and re-evaluate your payment capacity. But I guess my loan manager or even the underwriter valuably closed his(their) one eye.