In Exodus 3:18 Moses is commanded to gather the Israelite elders, go to Phara0h and say "יְהוָ֞ה אֱלֹהֵ֤י הָֽעִבְרִיִּים֙ נִקְרָ֣ה עָלֵ֔ינוּ וְעַתָּ֗ה נֵֽלֲכָה־נָּ֞א דֶּ֣רֶךְ שְׁלֹ֤שֶׁת יָמִים֙ בַּמִּדְבָּ֔ר וְנִזְבְּחָ֖ה לַֽיהוָ֥ה אֱלֹהֵֽינוּ" "The Lord, the God of the Hebrews appeared to us and now please let us go a journey of three days into the wilderness and we will slaughter to the Lord, our God."
But in Exodus 5:1, Moses changes the words when talking to Pharaoh and says "כֹּֽה־אָמַ֤ר יְהוָה֙ אֱלֹהֵ֣י יִשְׂרָאֵ֔ל שַׁלַּח֙ אֶת־עַמִּ֔י וְיָחֹ֥גּוּ לִ֖י בַּמִּדְבָּֽר" "So said the Lord, God of Israel, 'send out my nation and they will celebrate to me in the wilderness.'" Pharoah responds (Exodus 5:2) by claiming ignorance of the Lord, saying "מִ֤י יְהוָה֙ אֲשֶׁ֣ר אֶשְׁמַ֣ע בְּקֹל֔וֹ לְשַׁלַּ֖ח אֶת־יִשְׂרָאֵ֑ל לֹ֤א יָדַ֙עְתִּי֙ אֶת־יְהוָ֔ה וְגַ֥ם אֶת־יִשְׂרָאֵ֖ל לֹ֥א אֲשַׁלֵּֽחַ" "who is the Lord that I should listen to his voice to send out Israel; I don't know the Lord and also Israel I will not send out."
In the very next verse however, Moses reverts back to the message that God had told him to use and says "אֱלֹהֵ֥י הָעִבְרִ֖ים נִקְרָ֣א עָלֵ֑ינוּ נֵ֣לֲכָה נָּ֡א דֶּרֶךְ֩ שְׁלֹ֨שֶׁת יָמִ֜ים בַּמִּדְבָּ֗ר וְנִזְבְּחָה֙ לַֽיהוָ֣ה אֱלֹהֵ֔ינוּ" "the God of the Hebrews appeared to us and now please let us go a journey of three days into the wilderness and we will slaughter to the Lord, our God." This time Pharaoh doesn't deny any knowledge of God but instead accuses Moses and Aaron of distracting the Israelites from their task and being lazy.
The simple reading of the text implies that Pharaoh did not know who the God of the Israelites was but did know who the God of the Hebrews was. And unlike the God of the Israelites, Pharaoh had at least some level of respect for the God of the Hebrews.
Is is possible that Pharaoh did not know that the God of the Israelites was the same as the God of the Hebrews? Is this evidence that the term Israelite and Hebrew were not viewed are referencing the same people (i.e. that Israelites were a subset of Hebrews)?
And if there was a really a difference between the terms, why did Moses change God's message?