Syncretism is mixing religions (as doctrines, beliefs). Assimilating local traditions into one's religious rituals is not that.

"It can include assimilation of several originally discrete traditions, especially in theology and mythology, thus asserting an underlying unity and allowing for an inclusive approach to multiple faiths."

"...in the realm of religion, it specifically denotes a more integrated merging of beliefs into a unified system, distinct from eclecticism, which implies a selective adoption of elements from different traditions without necessarily blending them into a new, cohesive belief system."

"It provides an opportunity to bring beliefs, values, and customs from one cultural tradition into contact with, and to engage different cultural traditions."

https://en.wikipedia.org/wiki/Syncretism