How to set multiple spark configurations for single spark job

[#1]

I am dealing with a weird situation , where I have small tables and big tables to process using spark and it must be a single spark job.

To achieve best performance targets, I need to set a property called

spark.sql.shuffle.partitions = 12 for small tables and
spark.sql.shuffle.partitions = 500 for bigger tables

I want to know how can I change these properties dynamically in spark ?
Can I have multiple configuration files and call it within the program ?

[#2]

I believe you can achieve this by following the below sequence: 

1. spark.sql("SET spark.sql.shuffle.partitions=12")

2. Execute operations on small table

3. spark.sql("SET spark.sql.shuffle.partitions=500")

4. Execute operations on larger table