High-level programming abstractions (i.e. "middleware") primarily aim at: abstracting from heterogeneity and hardware complexity, simplification of (re-)programming, specifying system behavior in a post-hoc fashion. So far in the Wireless Sensor Networks (WSNs) domain the focus has been put mainly on the first two tasks and the application level of the last one. The meta-code approach we propose offers mechanisms to support low-level programming (e.g. time-sync, routing schemes, etc) on pre-deployed networks still requiring minimal knowledge of network characteristics. Its sole task is to provide tools to finely tune existing infrastructures with an "assembler-level" granularity in order to create task-specific highly optimized configurations. The meta-code is being designed taking into account specific requirements of WSNs, namely limited computational resources and power consumption.