Tampering with the reports as you have described is cheating and betrayal that is not permissible, and it leads to the consumption of people’s wealth unlawfully.
Everyone who takes part in this cheating is sinning.
The buyer should be told of whatever faults exist in the work that has been done, then if he accepts the work regardless, all well and good, otherwise the workers should fix it as you said.
Muslim (101) narrated from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “He who deceives us is not one of us.”
Al-Bukhaari (2079) and Muslim (1532) narrated that Hakeem ibn Hizaam (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The two parties to a transaction have the option (of cancelling it) until they part. If they are honest and disclose any defects, their transaction will be blessed, but if they lie and conceal defects the blessing will be erased.”
It should be noted that provision is something that has been decreed by Allaah before He created the heavens and the earth, so do not be tempted to seek provision by disobeying Allaah if it seems to be slow in coming.
The Prophet (peace and blessings of Allaah be upon him) said: “The Holy Spirit (Jibreel) has inspired to me that no soul will die until it has completed its appointed term and received its provision in full, so fear Allaah and do not be desperate in seeking provision, and no one of you should be temped to seek provision by means of committing sin if it is slow in coming to him, for that which is with Allaah can only be attained by obeying Him.” Narrated by Abu Na’eem in al-Hilyah from the hadeeth of Abu Umaamah; classed as saheeh by al-Albaani in Saheeh al-Jaami’, no. 2085.
What you must do is advise those who are in charge of the company, and explain to them that cheating is haraam and what its consequences are in this world, as it takes away the blessing, and in the Hereafter it brings punishment for wrongdoing and consuming people’s wealth unlawfully. If they respond, then praise be to Allaah, but if they do not respond, then you should ask to be moved to an area where no sin is involved. Otherwise, look for work elsewhere.
“And whosoever fears Allaah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).
3. And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allaah, then He will suffice him. Verily, Allaah will accomplish his purpose. Indeed Allaah has set a measure for all things”
We ask Allaah to grant you abundant provision and to bless your wealth for you, and to make you independent of means by that which is halaal so that you have no need of that which is haraam.
And Allaah knows best.