Exclusivity is a prime requirement in the official rules of many world religions. But my question stands in real life situations.
The literature on modern syncretistic practice is not extensive. We came across one tantalizing excerpt from an article by Jay McDaniel - Double Religious Belonging: A Process Approach - in the journal Buddhist-Christian Studies 23 (2003) p. 67:
Increasingly, Christians in the United States are turning to Buddhism for spiritual insight and nourishment. Many are reading books about Buddhism, and some are also meditating, participating in Buddhist retreats, and studying under Buddhist teachers. As they do so, they approach what might be called "dual religious belonging." The phrase itself can suggest at least three metaphors. We can imagine themWhat do you think?
(1) as people crossing a bridge into the world of Buddhism and who then return to Christianity with fresh insights; or
(2) as people with two intravenous tubes in their arms, one providing fluid from a Buddhist lineage and one providing fluid from a Christian lineage, for the sake of a more complete life; or, shifting to a more organic metaphor,
(3) as people with primary roots in Christian soil but with secondary roots in Buddhist soil, who receive anchorage and sustenance from both kinds of soils.
Shortly I will draw upon the third metaphor to suggest the desirability of a "taproot" as opposed to a "fibrous" approach for such double belonging, at least in its initial stages.