Capacitor

Some general recommendations:

- Do NOT change the capacitance value of your capacitor. The design calculations are based on its existing value.

- DO change it as long as you are INCREASING its voltage rating. Never any harm in increasing its voltage rating.

- Do NOT *EVER* replace a bi-polar capacitor with a polar one, otherwise it may blow up.

Oldhvymec

You CAN use polar capacitors as long as you connect them back to back like positives together or negatives together.  This will HALF the value of the capacitance however. So if you intend to make a resultant of 10 uF of capacitance, you will use TWO 20 uF connected back to back. 
So this is one way of kludging it.  Another point to think is the LONGEVİTY of the capacitors. Polar ones will most likely be electrolytics and will NEVER last as long as film capacitors hence adding another reason to not use polars.