There are things you can change easily in an SSIS package dynamically. The easy way to tell if you can is if they're in the list of properties under expressions for the source/destination or the datasource itself.

There are things you CAN'T change easily in an SSIS package dynamically, one of which is the metadata of the dataflow. The dataflow uses internal IDs based on the object that 'sources' the column to determine its type, value, and other items. There are third party objects out there that can allow you to have some variable source constructions, but even they are limited to having the same output results into the metadata (at least for used columns).

SSIS isn't meant to be that dynamic. In the same way that you need to write dynamic T-SQL to allow for major changes to queries, you need to write dynamic packages to account for variable metadata. This is nowhere near as easy as dynamic SQL however, and will require a pretty solid background in coding.