Praise be to Allaah.
It is not permissible to tamper with the date of
certification, because that involves deceit, lying and trickery towards
employers for no good reason.
If the companies have stipulated that they will only accept
new graduates, then you have to abide by this condition and it is haraam to
resort to trickery in order to get around it, because the Prophet (blessings
and peace of Allah be upon him) said: “The Muslims are bound by their
conditions.” Narrated by Abu Dawood, 3594; classed as saheeh by al-Albaani
in Saheeh Abi Dawood.
That is also because of the general meaning of the evidence
that deceit and lying are haraam.
We advise you to fear Allah, may He be exalted, and to do a
lot of righteous deeds and think positively of the Sovereign, the Most
Generous, Whose stores never run out, and all provision, health and success
come from Him.
We ask Allah to bestow His bounty upon you and provide you
with permissible, blessed work.
And Allah knows best.