Changing a column value based on a parameter

Hi all,

I am looking to do the following:

1. Create a list based parameter, so a list of manually entered values. It seems this is only doable at the data source level, which is a bit shocking to me. At the report level there are only what-if (limited numeric based) parameters.

2. Have a calculated field change dynamically based on whatever is chosen in that parameter. For example:

Say you have a list parameter, one choice is US Dollars, one choice British Pounds. The column (measure) would be something like this:

IF(currency_chosen_parameter = "US Dollars", dollars_in_US, dollars_in_british)

So basically have the measure change dynamically based on the value chosen in the parameter (note that while my example included changing a currency, my real life example is very different). 

I am shocked that Power BI doesn't seem to have that capability. List parameters are done at the source level, and you can't seem to change a (calculated) measure value based on the value chosen in a list parameter. Am I missing something?

Bonus question - is it possible to dynamically change a data type? For example, make it currency if it's over 1, else make it a %. Has anyone found a workaround for this kind of thing?