You can use the [MemRead] command to read from a memory block, after first creating the block from the file using [MemCreateFromFile]. If you were reading char, you could then put these together using [StrMerge]. That would give you a string that represented your float. In zscript the only numerical data type in float so there would be no need to do more than evaluate the string using [Val].
As for ‘displacing the tool in ZBrush’, you are limited in zscript to using the interface buttons or sliders, for example in the Tool>Deformation submenu.