functions.php

function wc_subscriptions_custom_price_string( $pricestring ) {
    $newprice = str_replace( 'every 3 months', 'per season', $pricestring );
    return $newprice;
}
add_filter( 'woocommerce_subscriptions_product_price_string', 'wc_subscriptions_custom_price_string' );
add_filter( 'woocommerce_subscription_price_string', 'wc_subscriptions_custom_price_string' );