Pine script: Switch trendline based on if statement

How do I set my trendline color and plot based on an if statement i.e. if stock data is > 1 year then use trendline 1 else use trendline method 2:

trend_1 = sma(close, 15)
trend_2 = sma(close, 30)

bearish = true

for i = 0 to trendConfirmationLength - 1
    bearish := bearish and (close[i] < trend[i])

bullish = not bearish

// Set the color of the plot based on whether we are bullish (green) or not (red)
c = bullish ? color.green : color.red

// Plot the trend line
trend = 
if (len(close) > 252)
   trend_1
if (len(close) < 252)
   trend_2

trend_plot = plot(trend, title='Trend', color = c)

Thanks