What is the ruling on working in a shop that sells office supplies and products bearing crosses, with an attempt to conceal the crosses by rotating the boxes? And does this work amount to disbelief and apostasy from the religion?

This act is neither disbelief nor apostasy. There is no apparent prohibition against selling tools bearing flags of countries that include a cross, because flags and emblems are secondary and not the intended object of the merchandise. "What is secondary is not singled out for a ruling," and "what is tolerated implicitly in a thing is not tolerated explicitly." Furthermore, the widespread prevalence of such items and the difficulty of avoiding them necessitate leniency, for "when a matter becomes difficult, it expands." Wearing something that contains the image of a cross is disliked (makrooh tanzeehan) by the majority of scholars, but not forbidden.