How to change an installed extension without it getting disabled?

[Balaco]

I installed an extension, and saw that it need a small adjust for my
preferences for it.

I opened its code, changed and saved. After doing that, I restarted
Firefox, but it disabled the extension! How can I do?

If I remove files META-INF/mozilla.rsa , META-INF/manifest.mf and
META-INF/mozilla.sf from its .xpi file, solves my problem?

Or, if there is a way to disable this "disable if it cannot be verified"
for add-ons, please point it to me.

[Balaco]

No, removing the META-INF folder does not work. I want to install and/or
modify whatever .xpi add-on and have it always enabled, unless *I*
disabled or remove it. How can I do it?

[Balaco]

hahaha... it was not so easy to find, but there is a page with some
interesting information:

https://support.mozilla.org/pt-BR/kb/extensoes-assinadas-do-firefox?as=u&utm_source=inproduct#w_desconsiderando-assinatura-de-extensaies-usuaarios-avanadados

or (possibly for the same address) this shorter link:

http://mzl.la/1J7Lcsp

(complain with Mozilla that it did not give me a way to copy that
address for the English page)

The answer I wanted is:

Go to about:config page and change the

xpinstall.signatures.required

setting to false.