Sometimes its okay to change the liturgy, sometimes it isn't.

Before we had shuls, prayers took place in the Temple where a liturgy was often celebrated by the Levites as sacrifices were brought. One such prayer was the recitation of Psalm 44, which speaks of a slumbering God who no longer performs the miracles our ancestors saw. An excerpt:

9 But now you have rejected and humbled us;
you no longer go out with our armies.
10 You made us retreat before the enemy,
and our adversaries have plundered us.
11 You gave us up to be devoured like sheep
and have scattered us among the nations.
12 You sold your people for a pittance,
gaining nothing from their sale.

13 You have made us a reproach to our neighbors,
the scorn and derision of those around us.
14 You have made us a byword among the nations;
the peoples shake their heads at us.
15 I live in disgrace all day long,
and my face is covered with shame
16 at the taunts of those who reproach and revile me,
because of the enemy, who is bent on revenge
[ ]
23 Awake, Lord! Why do you sleep?
Rouse yourself! Do not reject us forever.
24 Why do you hide your face
and forget our misery and oppression?

According to the Gemarah this Pslam was recited by the Leivites every day as sacrifices were offered. The Gemarah also says the practice was instituted during times of suffering. In The Sages, Binyamin Lau suggests the custom owas established as a response to Selucid persecutions. For the Jews who lived through those terrible years, it must have seemed as if God was sleeping.

Year later (probably around 120 BCE)  Yochanan Kohen Godol abolished the prayer (Maaser Sheni 5:15) As Lau argues, the times had changed. A new era of peace and tranquility had begun (see back story below), and it was no longer appropriate to speak of a sleeping God who ignored prayers and left His people defenseless. Though the facts of currents events had previously supported the words of the Psalm, by the time of YKG the facts of current events had changed and the prayer could no longer be said.

There's an analogy here to events in our own time. Once upon a time, there were clear advantages to being a man. In the ancient world, women were slightly better than slaves, with no real legal rights. In such a time and place it made sense to thank God each morning "for not having made me a woman." Those days are over. Women are now full citizens of nearly every country, with rights and opportunities their ancient grandmothers never imagined. Just as Yochanan Kohen Godol abolished the Temple prayer on the grounds that the times no longer justified it, isn't it time for someone of YKG's stature to do the same with our out-of-date morning blessing?
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Here is some of the historical back story:  Yochanan Kohen Godol,  identified by scholars as John Hyrkenus, was perhaps the most successful Hashmonian leader. Acting as Prince of Judea, he negotiated a truce with the Selucids, and later took advantage of the collapse of their empire to expand his own kingdom, destroy the rival Samaritan Temple on Mount Grizim, and force the neighboring Idumeans to convert. Read more about the achievements of Yochanan Hyrcanus on Wikipedia

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