On a fixed mortgage, i could pay extra payments (or a one time lump sum payment) and apply it towards principal.

The note investor who thought interest is paid on the original principal rather than the unpaid principal balance.  

Salavatore,I have been doing NNN about 21 years as a principal broker and an investor.

Here's the terms:FOR VALUE RECEIVED, XXXXX a limited liabilitycompany (hereinafter referred to as "Maker*), hereby promises to pay to MY NAME,whose address is redacted (hereinafter referred to as"Holder"), or order, the principal sum of $XXX,000.00 in legal tender of the United States, accruing interest at an annual rate of 18.0%.

Here’s my question: Should I use my w-2 income to pay down a lot of principal and re-try to obtain that HELOC?

Here's a https://www.irs.gov/businesses/cost-segregation-audit-technique-guide-chapter-4-principal-elements-of-a-quality-cost-segregation-study-and-report to the IRS website noting specific items that are included in the cost segregation study report. hmm, that website is a 404 error.  

You'd analyze it as a "cash purchase" and add a special expense category for your principal & interest payment.  

I think paying off a loan with a high interest rate debt and adding to the principal is one way to stay liquid within the property. 

The first monthly interest installment of xxxxx due on or before April 15, 2024 and continuing in like consecutive monthly interest installments of this amount for a total of one (1) year or twelve (12) payments at which time the entire unpaid balance, including Principal, accrued but unpaid interest, will become due and payable.

This will lower interest costs and free up future cash flow for reinvestment or reserves.Tax Planning: Work with a CPA to mitigate tax impacts from principal-heavy payments and potential gains.