People may say that but it is not true, there is only one God and He is God of both the Old and New Testaments.
In the OT there is mentioned about not eating food sacrificed to idols. Later, in the NT it says that there is only one God, idols do not exist, so therefore it would be acceptable to eat food that was once sacrificed to idols.
Now, a weaker brother or sister may still adhere to the admonishment not to eat food sacrificed to idols even though that person is now aware that there is only one true God and idols are dead and worthless. It states that it would be wrong for a person. now aware, that it acceptable to eat the food that was once sacrificed to idols, but should refrain from doing so in front of the person who believe that it is still sin to do so as that may tempt that person to eat that food and therefore sin. I believe that this would be a classic example of scruples.
God changes not but one's understanding of God and of scripture may progress in a more spiritually sound and positive direction. In the book of Isaiah there is an explanation of spiritual growth. "Come now, and let us reason together...line upon line, precept upon precept. A little here, a little there". God changes not but what does change is the inside of our hearts in discerning what is right from wrong and a desire to change in a way that is aligned with God's will and desire. This is called repentance and eventually leads to sanctification.