Why did Necho make Yehoyakim king?
Radak (Melachim II, 23:33): It was so Yehoyakim would be his servant, and know that he rules due to Necho.
Malbim (Melachim II, 23:34): Refer to 36:3:4:2.
Why did he change his name?
'Rashi': Kings normally give to their servants a name that they like, e.g. Pharaoh called Yosef "Tzafnas Pane'ach" (Bereishis 41:45), Moshe called Hoshe'a "Yehoshua 1 " (Bamidbar 13:16), and Sar ha'Sarisim gave names to Daniel, Chananyah, Misha'el and Azaryah (Daniel 1:7).
Radak (Melachim II, 23:34): It was so Yehoyakim would know that he rules with Pharaoh Necho's permission, and his kingship and [even] his name is [from him, and] not from his mother 2 .
