To change the parameters you want passed to your processes, I believe that you must edit the .xml file of your process. For example,
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.0">
<context>
<input/>
<output/>
<macros/>
</context>
<operator activated="true" class="process" compatibility="5.0.10" expanded="true" name="Process">
<process expanded="true" height="145" width="212">
<operator activated="true" class="generate_data" compatibility="5.0.10" expanded="true" height="60" name="Generate Data" width="90" x="112" y="30">
<parameter key="number_examples" value="10"/>
</operator>
<operator activated="true" class="write_csv" compatibility="5.0.10" expanded="true" height="60" name="Write CSV" width="90" x="271" y="39">
<parameter key="csv_file" value="C:\Users\wessel\Desktop\gendata.csv"/>
</operator>
<connect from_op="Generate Data" from_port="output" to_op="Write CSV" to_port="input"/>
<connect from_op="Write CSV" from_port="through" to_port="result 1"/>
<portSpacing port="source_input 1" spacing="0"/>
<portSpacing port="sink_result 1" spacing="0"/>
<portSpacing port="sink_result 2" spacing="0"/>
</process>
</operator>
</process>
You can see that for the write_csv operator, the value contains the path of the file to be written to. Changing the parameters as you describe would involve writing a script to get the values from the user, edit the corresponding values in the .xml file to these desired values and then throwing the process at RapidMiner.