Trying to show UTCI heatmap on a street surface, and later replace the cell values received with manually inputted temperature

So I have honeybee and ladybug. My project entails taking the surface temperature of streets in a grid. That information I can get from the epw file. However, I want to later modify this. I want to replace cell values that are on the street with a temperature -2 C. Meaning if one cell on the grid that is on the grid is 25 C, I want to create a script that essentially says, “If this cell is near a canal line, -2C”. I want to introduce canals that are in the street grid, some taking over completely, some being scattered.