A new build of your EA arrives — a bug fix, a new filter, a fresh licence. Replacing it sounds like dragging one file over another. The risk is everything attached to the old version: the inputs you tuned, the trades already open, and the magic number that ties the two together. Get the order wrong and you can detach a working system from live positions, or restart it on default settings. Here is how to swap versions without losing either.
What can go wrong
- Your settings. Inputs you tuned over months live in the EA's parameters, not the file. Drop in a new build and reattach, and it loads defaults unless you reload your set file.
- Open trades. Detaching an EA does not close its trades, but the new version may not recognise them. If the magic number changes, the fresh build treats existing positions as strangers and stops managing them — no trailing stop, no take-profit, nothing.
- A silent default change. A new version can ship with a different default lot size or risk percentage. Miss it and the first trade is the wrong size.
Before you touch anything, save your set file: right-click the chart, then Expert Advisors, Properties, Inputs, Save. That one file is your settings. Without it, an update is a reset.
The safe order
- Save the set file from the running EA, as above. Name it with the date.
- Note your open trades — tickets, magic number, lot sizes. A screenshot is fine.
- Back up the old EA file and copy it out of the MQL folder so you can roll back.
- Check the magic number the new version uses. If it differs from the old one, set it to match, or the new build will ignore your live trades.
- Copy the new file in, then refresh the Navigator or recompile in MetaEditor.
- Reattach and load your saved set file. Confirm every input, especially lot size and risk.
- Watch the first few ticks on live before walking away.
A worked example
You run an EA on a £10,000 account at 0.10 lots per signal, tuned over six months. A new version lands. You drag it in, reattach, and walk away — without loading your set file. The new default is 1.00 lots. The next signal opens ten times your intended size. On a 30-pip stop that is roughly £270 at risk instead of £27. The set file you skipped took ten seconds to save.
Now the magic number. The old build had three trades open, worth £180 floating. The new version uses a different magic number and never adopts them, so their stops sit unmanaged until you close them by hand. Matching the magic number first would have carried them across untouched.
Test before live where you can
If the update is more than a small fix, run the new version on a demo account with your set file for a day or two first. You are checking that it reads your settings and manages trades the way the old one did, not chasing profit. A version that behaves differently on demo will behave differently on your money.
The Karnek note
Karnek watches from outside the terminal, read-only, so an update never risks your monitoring — the history and open trades stay visible across the swap. It reads what your EA does, and it can never place, change or close a trade itself.
Written and reviewed by the Karnek Research team. Last updated August 2026.
Educational content only - not financial advice. Past performance does not predict future results. Trading carries significant risk.