Disclaimer: I got a B in physics 242, and that was the last time I actually did this kind of stuff. I'm piecing together what I remember and what I find on wikipedia here.
First off, according to wikipedia, the resistance of air at sea level at 20C is 1.30*10^16 to 3.30*10^16 ohm*meters.
Not many things resist electricity better than that - teflon, fused quartz, polyethylene terephthalate... There are things considered perfect insulators for practical systems that are actually more conductive than air. Oven dried wood, for example.
The only way to change the conductivity of a gas is to change the composition of the gas, and... Well, gasses are just very, very bad conductors in general until you ionize them (which is what lightning does), at which point they're suddenly very, very good conductors (air included), so you're just moving between different kinds of awful. However, that's not what chemtrails supposedly do. They add aerosols or particulates. That doesn't change the conductivity of air.
What it does do is give a series of more conductive channels, but the electricity still has to pass through air between them. Aluminum and barium are both really good conductors (2.82*10^-8 and 3.32*10^-8 respectively), but the math is a pain, so let's pretend they're both perfect conductors (0).
Now, the effect of aluminum and barium aerosol or particulate on the atmosphere's conductivity is basically how much they reduce the bolt's path to the ground - the charge will have no resistance where it passes through a particle, but will return to full resistance in the air.
Example: If you have a tesla coil 1 meter away from a target, but only enough power to create a 900 cm arc, if you could fill 10% of the air between the coil and the target with particles of our hypothetical perfect aluminum, you'd get a spark. It would be 900 cm of air arc with 100 cm passing through the aluminum particles. If I'm remembering right, whether that 900 cm is in one step or 10 steps of 90 or 100 steps of 9 or a thousand steps of 0.9, the cumulative resistance adds up the same.
This would be a pretty thick cloud of aluminum dust. Once the spark goes off I imagine you'd have a fire on your hands, maybe even a dust explosion.
If you used aluminum fibers it would be better, since their length means they will provide longer conduction. Particles and droplets basically need to fill the air, but fibers could be much more diffuse. You'd still need a lot of them, but for our tesla coil, a handful of chaffe or just shredded wires would probably do it (note: don't use an actual handful if you value counting to five on one hand).
But this then comes to the problem that actual lightning jumps thousands of meters (google tells me the average is around 5 km). Google also tells me the average thunderstorm is 16 km in dimater, meaning you need very thick chaffe in a volume on the order of 201 square kilometers up to whatever height the lighting originates from. Again, google tells me 1-2 km, meaning 200-400 cubic kilometers of chaffe deployed in densities far exceeding anti-radar use, to get maybe a 10% increase in lightning, which is less than the variation between otherwise similar storms. And that's assuming the storm is stationary, which does happen but is rare - they can move faster than the surface winds below them, some squall lines have been timed at 50-100 mph.
And statistically speaking, lightning is not that dangerous. There's a lot of things in thunderstorms that kill people - tornadoes, wind, rain, and hail all cause more property damage and deaths than lightning. Wind even causes more power outages than lightning itself.
If you want to make a storm more dangerous, this is not the way. You want to add energy, not make it easier to dissipate. More water, more heat, not more lightning. And storms are unbelievably powerful as it is. As I showed in the thread about artificial storms, we as a species simply don't have the ability to make enough power in one place to evaporate the water it takes to affect a storm.