Universalize doesn't have the sense 'to create a universe' as the productive suffix -ize (-ise) modifies the word universal, not universe.
The correct formation would be universize (universe + -ize) for the meaning 'to create a universe'; however, it is not defined in any dictionaries and it is not a concept that necessitates a single word. Although, you can use it as a nonce word for your needs.
OED says the sense "Of or relating to the universe in general or to all things in it" for universal is poetic or rhetorical, and now rare. And surprisingly, OED also lists an obsolete sense of universal meaning 'The universe'.
There is the word cosmogony with the meaning of 'the creation of the universe (cosmos)' but it is generally used in extended senses like the study of the origin of the universe or the theories/models involved within that context. As its etymology suggests:
From Ancient Greek κοσμογονία (kosmogonía), from κόσμος (kósmos, “world”) + γόνος (gónos, “creation”). - Wiktionary
I surmised that cosmogonize could mean 'to create a universe' but it has another meaning related to the extended senses (and the right formation could be 'cosmosize' for the meaning 'to create a universe'):
cosmogonize: To theorize a cosmogony - Wiktionary
Although, you could possibly use cosmogonize in the sense 'to create a universe', perhaps within the right context in a fictional story or figuratively. I could also find instances of cosmosize in Google Books.
Additionally, OED lists cosmize as a rare word, formed as cosmism n. + -ize suffix. It has a slightly different meaning and it is used figuratively in the only citation provided:
transitive. To make into a cosmos.
It's the duty of man to try..to cosmise his own particular little corner of it.
1884 G. Allen Philistia III. 28