Not so fast, old man! Notwithstanding this IS a forum for Doing-It-Yourself, it appears you are no cost accountant!
I advance the following rebuttal IN GOOD HUMOR:
It all depends on the relative cost of labor. The custom cable costs $50. A connector costs $5 and it takes only ten minutes to replace one connector with another. Doing it yourself saves $45 of the cost of a $50 custom cable. As Ben Franklin observed, "a penny saved is a penny earned." In effect, one "earns" $45 by doing it himself, or having an employee do it.
The $45 saved in 1/6 of an hour translates to an hourly rate of $270, which means one pays the custom shop at the rate of $270 an hour to replace an XLR connector. No rational businessman would pay $270 per hour for such a simple task. A rational businessman would hire an employee to complete the task for one-tenth of that cost, or, even better, do it himself at "no cost" over his lunch hour or during half time of the big game on Saturday afternoon. When working, I billed $250 per hour for my time. Even so, it would make good financial sense to do it myself on a coffee break, as I would, essentially, break even at comparing my hourly rate against rate the effective hourly cost of the custom cable.
In fact, I followed my own advice to great advantage. I operated my professional office with NO employees for nearly a decade, employing optical character recognition (OCR) and computer speech recognition software to supplant a secretary. Employees are, if you pardon a crude, yet effective expression, "financial parasites." A professional must work longer and harder, and charge more per hour, to pay their salaries in addition to his own. Replacing employees with technology can be a very cost-effective trade. I comfortably retired on my 50th birthday by leveraging technology against the cost of labor, eliminating employee salaries, employment taxes, unemployment tax, worker health insurance, worker injury compensation insurance, and more; working smarter, not harder, managing fewer client matters and keeping more of my hourly fee for myself. In other words, I was able to keep the share I would have otherwise paid for support staff.
Bottom line - considering the big picture, soldering a new connector over the lunch hour yourself may be substantially more profitable than paying $50 to the custom cable shop.
N'est ce pas, mon ami?
Again, you are no cost accountant.
I suspect you meant to say "write off" in the tax year of acquisition. One "amortizes" or "depreciates" an asset over a longer period, usually multiple years.
Besides, if one fully writes-off or depreciates an asset, and later resells it for cash, the proceeds of sale are "depreciation recaptured" and TAXED as regular INCOME, and are, occasionally, subject to capital gains TAX. Add the cost of having your accountant or CPA figure it, and you may better just scrap it or donate it to charity.
Once again, it is not as cut and dried or as simple as some may suggest !!
All in good fun - and yet sorta serious, too. Happy trails to you. James