I think there are a couple of options; they might not be ideal but could work.
If by "to activate" the script you mean to authorize it, you can make a trigger that auto runs a function inside the script once the spreadsheet is open https://developers.google.com/apps-script/guides/triggers/
Having said that, to run your script in another spreadsheet and make it globally available to you, you could use libraries; take a look at this other link https://developers.google.com/apps-script/guides/libraries.
- First you create your library in a separate script (this would need copy paste).
- Once you have your library, you can import it to other Apps Script projects or spreadsheets.
The downside to this is that you would still need to open the script editor and write minimal code to import your library, so it might not be exactly what you want but I hope it helps.