zigbee: moving data from mqtt to influxdb - transforming strings to integers

After some first steps with zigbee devices and storing the data in an influxdb, i noticed that string values are suboptimal for building graphs. 

Moving the data from mqtt to influxdb was done with telegraf:

https://www.influxdata.com/time-series-platform/telegraf/

And i was wondering, how i can change string to integers, but this i very easy:

  [[processors.enum]]
    order = 2
    [[processors.enum.mapping]]
      field = "state"
      [processors.enum.mapping.value_mappings]
        "ON" = 1
        "OFF" = 0
    [[processors.enum.mapping]]
      field = "contact"
      [processors.enum.mapping.value_mappings]
        "true" = 2
        "false" = 1
    [[processors.enum.mapping]]
      field = "tamper"
      [processors.enum.mapping.value_mappings]
        "true" = 1
        "false" = 0
    [[processors.enum.mapping]]
      field = "water_leak"
      [processors.enum.mapping.value_mappings]
        "true" = 1
        "false" = 0

Next problem: if the column "water_leak" was already added inside your influxdb, you can not add numbers - so you have to drop the table and loose your data...

(This is not the full truth: you can export the data via a select to a file and insert the data afterwards - with the appropriate numbers...)