Username truncation affects the original variable.

[DasBrain]

Reproducer:

Edit the set username of the config to something like this

set dasbrain's-awesome-configuration-template-name tcl9eggdrop
putlog "DBG: dasbrain's-awesome-configuration-template-name: ${dasbrain's-awesome-configuration-template-name}"
set username ${dasbrain's-awesome-configuration-template-name}
putlog "DBG: Username: $username"
putlog "DBG: dasbrain's-awesome-configuration-template-name: ${dasbrain's-awesome-configuration-template-name}"

Observe when starting eggdrop it outputs:

DBG: dasbrain's-awesome-configuration-template-name: tcl9eggdrop
DBG: Username: tcl9eggdro
DBG: dasbrain's-awesome-configuration-template-name: tcl9eggdro

The set username ${dasbrain's-awesome-configuration-template-name} modifies dasbrain's-awesome-configuration-template-name variable.