I think it could be done with very little in changes. Solano López wasn't an awful military leader. He recognized the weaknesses in his own forces and South Americas. He bought European Weapons and adopted French/Prussian training.
Maybe in a quick war he could have succeeded. The real issue was how he ran the country and his international diplomacy. His economy just couldn't handle any long term conflict. The Requirement by Service was needed to make up for numbers, but it also led to famine and issues with production of needed goods. Opening Paraguay to European interests could help, but without access to the sea, it's not realistic to assume real investment. The better option is to adopt the agricultural practices of Britain. Fertilizer, Crop Rotations and such. Building an industry, maybe the use of Looms/Water Wheels could help build an industry.
Internationally the biggest issue in this conflict was bringing in Brazil. I would argue though, that Brazil's intervention was almost certainly going to happen, following Lopez interference with Uruguay. Uruguay was the focus of both Brazil and Argentina. Both sides worked on bringing the nation into their sphere of influence. Lopez attempt to enter into this is what arguably made Paraguay a target of Brazil.
In theory if the Paraguayan army had done better and quicker, even with trespassing on Brazilian territory, Brazil might have left them alone. It was attempting to topple the pro-Brazil Uruguay Government that put things badly. The issue you have is even with all these changes, Argentina solo could still win the war in a prolong conflict. Lopez was not competent enough to avoid being caught in a drawn out conflict.
Maybe in a quick war he could have succeeded. The real issue was how he ran the country and his international diplomacy. His economy just couldn't handle any long term conflict. The Requirement by Service was needed to make up for numbers, but it also led to famine and issues with production of needed goods. Opening Paraguay to European interests could help, but without access to the sea, it's not realistic to assume real investment. The better option is to adopt the agricultural practices of Britain. Fertilizer, Crop Rotations and such. Building an industry, maybe the use of Looms/Water Wheels could help build an industry.
Internationally the biggest issue in this conflict was bringing in Brazil. I would argue though, that Brazil's intervention was almost certainly going to happen, following Lopez interference with Uruguay. Uruguay was the focus of both Brazil and Argentina. Both sides worked on bringing the nation into their sphere of influence. Lopez attempt to enter into this is what arguably made Paraguay a target of Brazil.
In theory if the Paraguayan army had done better and quicker, even with trespassing on Brazilian territory, Brazil might have left them alone. It was attempting to topple the pro-Brazil Uruguay Government that put things badly. The issue you have is even with all these changes, Argentina solo could still win the war in a prolong conflict. Lopez was not competent enough to avoid being caught in a drawn out conflict.