If Spear-EW can carry an effective EW suite a Tomahawk can fit one in, in addition to its main payload.
Well that depends on the definition of "effective". SPEAR EW is basically the payload is the EW device itself so it will act like MALD.
Tomahawk well.. I wonder. how much electrical power can be made available from the Engine. Or whether space can be made for it.
Let's say a terrain bounce deception jamming. One would need some form of ESM and antenna + transmitter for it. Or one could forgo the ESM we can assume the Enemy Radar SAM can be located and tracked real time from 3rd party and downlinked via the same Satcom antenna tomahawk use.
That left us with the transmitter. Potential radar SAM's are something like X-band maybe or even mm Wave. So one would need some form of array. with some size so it can be steerable electronically. This can add space requirement. as some part of the skin needs to be replaced with one with radome property.
and the power requirement. Since terrain bounce are deceptive. then it may not need the same amount of power a noise jammer needs. One can perhaps get away with 100-200 Watt of emitted power. If this is supplied from say a solid state device it the power requirement (assuming 33% PAE A-class for linearity of the signal) Would be about 303 to 606 Watt. the supporting electronics may add about 20% more so 60 to 121 Watt. So in total the electrical power requirement would be about 363 to 727 Watt.
The generator in case if its dedicated would weigh about 0.5-0.6 Kg or maybe adding 1 Kg at most. but again, can space be made. Otherwise a new generator would be needed.
So basically it might have to be a new build, instead of retrofitting.