Can a plant be programmed to produce any arbitrary object?
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1) Any material have some physical limitations and living tissue are not exceptions. A plant cannot resist to very high pressure without changing shape for example. Outside of these problems of material sciences I think the major considerations are technical…

2) It is possible to influence the shape of a plant by changing its DNA code, changing its physical and chemical environment (micro or macro environment) or by injecting some substance. Today we might be able to influence the number of branching of certain plants species for example. But we are terribly far from having enough knowledge in biology (in genotype-phenotype map, in biochemical pathway) in order to transform a dandelion into a shopping mall! Even we had already described all chemical pathway linking genes to phenotypic traits, it is immensely more complex to think of which kind of DNA sequence might transform a plant into something that is so different.

I don't know if anyone has ever created a totally synthetic (and not copied from already existing sequences) DNA sequence and could predict the impact it would have on the organism phenotype. Some people were able to create a totally artificial self replicating RNA though.

Note: Some people play with the properties of the DNA molecule in order to create various tissues. This might interest you as well.

One can highly improve this answer by giving some results of studies on synthetic life.