No, you're not in the place to decide for yourself what the meanings of words are. That is actually a thoroughly worldly, progressive (in the negative, left-wing sense) approach to language.
That's good. So do the vast majority of theologians and Bible experts, such as Dr. Michael Brown.
This undermines your whole position. If "God does not change" and "there was only God's revelation of what is true," then
'echad means what it means, and what it means is simply "one." It
can refer to a compound unity, but only if the context shows that that is the case. It does not always refer to a compound unity, as these verses show:
Gen 2:21 So the LORD God caused a deep sleep to fall upon the man, and while he slept took
one of his ribs and closed up its place with flesh. (ESV)
How many ribs?
Gen 10:25 To Eber were born two sons: the name of the
one was Peleg, for in his days the earth was divided, and his brother's name was Joktan. (ESV)
How many sons were named Peleg?
Gen 42:13 And they said, “We, your servants, are twelve brothers, the sons of
one man in the land of Canaan, and behold, the youngest is this day with our father, and
one is no more.” (ESV)
How many men fathered the twelve brothers? How many are no more?
Given that
'echad is used in the OT 968 times, there are numerous additional examples I could give that show it is also used to simply mean one and does not refer to a compound unity.
It also seems that you may not understand just what progressive revelation refers to. But that is another discussion.