Question: is it permissible to work in the jahili legal system composed of man made laws with the pretext of helping Muslims and defending them if they were to be subjected to questioning by the tawaqit?
Answer: it is not permissible if it means following certain laws or systems which defy the law of Allah.
If he were to work using laws that defy the Sharia willingly, knowing that it is against the Sharia: Then this is kufr and apostasy and belief in the Tagut(instead of Allah)-may Allah protect us from that-Allah says:
ألم تر إلى الذين يزعمون أنهم آمنوا بما أنزل إليك وما أنزل من قبلك يريدون أن يتحاكموا إلى الطاغوت وقد أمروا أن يكفروا به
“Have you seen those (hyprocrites) who claim that they believe in that which has been sent down to you, and that which was sent down before you, and they wish to go for judgement (in their disputes) to the Taghut (false judges, etc.) while they have been ordered to reject them.”
Surat An Nisa 4:60
But if he were being an attorney for and defending Muslims without committing disbelief or sin nor being satisfied with (certain) rules nor moving upon that way,and not under the man made Laws of ignorance:there is no objection.
Based on the Hadith: “whomever of you who is able to benefit his brother should do so”.
And the Saying of Allah:
فَمَن يَعْمَلْ مِثْقَالَ ذَرَّةٍ خَيْرًا يَرَهُ
So whoever does an atom’s weight of good will see it,
Surat Az Zalzalah 99:7
And the Hadith: “The Muslim is for a Muslim a structure (support)”
And other than these.
So based upon that, It is not permissible,and the first answer becomes the questions response, rather they be patient as was the case of the Sahaba when they were being persecuted by the tawaqit of Quraish in Makkah, The messenger of Allah did not, Allah forbid, commit kufr or apostasy in order to defend them, rather they were to be patient or migrate to a safe place,until jihad was prescribed or deliverance would come.
Shaykh Ali Khudayr ibn Khudayr