Altering the print bed temperature at different layers
The actual problem you are facing is bed adhesion, the proposed solution (in your question) shouldn't be the preferred solution to get your parts to stick to the plate/glass as plastic shrinks as it cools down. Note that a 5&nbsp;&deg;C temperature drop after the first layer usually isn't a problem, but larger temperature differences or shutting off the heat completely will cause your parts to come off the glass.

Note that PLA requires a temperature of about 60&nbsp;&deg;C (for adhesion as this is close to the glass temperature where the plastic is soft; however, note that PLA can be printed on cold bed surfaces on suitable bed surfaces). The slate of glass is an insulator, so it is perfectly possible that you need to set the bed at a higher temperature to get 60&nbsp;&deg;C at the surface of the glass plate. When the lower layer deforms the bed temperature is too high.

As you are using Cura, there is a plugin available called TweakAtZ, nowadays this is a default plugin. How to use this is described in this anser (on question "How does one use a heat tower?"); instead of changing the hotend temperature you will need to modify the bed temperature instead (using M140).

To solve the actual problem, you need to prepare the glass by cleaning it properly, use a level bed with a correct initial nozzle to bed distance for Z=0 (usually thickness of a plain paper sheet A4/Letter) and an adhesive like hairspray, glue stick or a dedicated adhesion spray like 3DLAC or Dimafix. I'm using 3DLAC for several years (for PLA and PETG; Dimafix is supposed to be more sticky at higher temperatures, so for ABS for instance) and never had any problems with adhesion on properly levelled beds. See this answer for another user's experience.

An OctoPrint solution using event as you suggest is not recommended. This is the config.yaml, e.i. the configuration of the print server, not a print instance option file. Furthermore, there are yet no plugins that can handle additional code when the head reaches a certain (layer)height. This is pretty tricky if you use Z position detection when the head also can hop, such code should be inserted by the slicer instead.



Related to your question are the answers on question: "Why keep the bed heated after initial layer(s) with PLA (or PETG)?".