Why not bring cyanobacteria and fertilizer to the atmosphere of Venus to improve conditions for life there by producing oxygen ?
Planetary protection could be a reason. According to Wikipedia:
Planetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of a sample return mission.
The missions are categorized into 5 groups and Venus is classified into Category II, implying no requirements for bioburden reduction or sterilization of equipment, supposing that there is only a remote chance that contamination by terrestrial microorganisms could jeopardize future explorations.
Only a few scientists have speculated that thermoacidophilic extremophile microorganims might exist in the lower-temperature, acidic upper layers of the Venusian atmosphere. It has been speculated that the clouds there could contain chemicals that can initiate forms of biological activity, like sulfur allotropes, but it is very unlikely that there will be Venusian microorganisms that use water and carbon dioxide for their existence.
So the biosignatures for instance that the Venus Atmospheric Maneuverable Platform will look for will be very different from those from the introduced cyanobacteria and consequently they will not jeopardize the explorations of the existence of Venusian life in the cloud region.
Cyanobacteria are a group of photosynthetic bacteria who use the energy of light to synthesize organic compounds from carbon dioxide, producing oxygen this way.
Nostoc commune is a colonial species of cyanobacterium which forms a gelatinous mass with other colonies growing nearby and in some cells nitrogen-fixing occurs. It is able to survive in extreme conditions in polar regions and arid areas. The cells also contain pigments that absorb ultraviolet radiation, which enables it to survive high levels of it. A dessicated colony is resistant to heat and to repeated patterns of freezing and thawing.
Nostoc commune can also withstand acidic exposure
So it seems that Nostoc commune could be a good candidate for surviving the harsh conditions within the cloud layers if it could be supplied with the necessary trace elements. The sticky biofilms that it produces could be supported by a mattress-like shape made of silica aerogel to keep it buoyant and to supply it with those elements.
The fertilizer could be delivered mainly in the form of hydroxides like KOH, Ca(OH)2 and Mg(OH)2 that would react with the suluric acid in the clouds to form the required water and sulfates.
The big question would be if the biofilms could float themselves outside the supporting mattress, feeding on the droplets of water with fertilizer.
Summarized, the water used by the cyanobacteria will be recycled eventually and the produced oxygen will accumulate and CO$_2$ removed !
Could not one trip for cyanobacteria to the atmosphere of Venus be a giant leap for life ?