When using the setblock command to replace a command block, the command will successfully execute, but return the message "The block couldn't be placed". If run from a command block, it will also fail to trigger comparators, but it will successfully trigger chain command blocks.

In the attached example image, blocks are as follows
Block A - Command set to /setblock 196 64 148 air
Block B - Test block to be replaced (at 196 64 148)
Block C - Test comparator output (command: /say Comparator)
Block D - Test chain output (command: /say Chain)

When block A replaced block B, block D triggers properly, but the comparator fails to trigger block C. If block B is anything other than a command block, both blocks C and D trigger properly. Block A (setblock) will fail if block B is any type of command block (chain, repeat, impulse, conditional, etc)