Short answer. No. Article 1212 says each one of the solidary creditors may do whatever may be useful to the others, but not anything which may be prejudicial to the latter. So you can take steps that benefit the whole group, but you cannot lawfully take an action that helps only you while harming your fellow creditors.
What the law says
Each one of the solidary creditors may do whatever may be useful to the others, but not anything which may be prejudicial to the latter.
Civil Code, Article 1212 — Useful and Prejudicial Acts of a Solidary Creditor. Read the full provision →
Useful acts yes, prejudicial acts no
In a solidary credit, any one creditor may demand and collect the whole debt, so the creditors are deeply intertwined. Article 1212 draws the line on what one of them may do alone: Each one of the solidary creditors may do whatever may be useful to the others, but not anything which may be prejudicial to the latter. The rule has two halves. A single creditor is free to act when the act benefits the group — for instance, taking a step that preserves or advances everyone's claim. But he is not permitted to act in a way that damages his co-creditors' interests. Helpful, yes; harmful to the others, no.
Why one creditor is restrained
Solidarity gives each creditor great power — including the power to receive full payment — but that power is held for the benefit of all, not as a private windfall. Each creditor ultimately owes the others their respective shares of what is collected. If one were free to take prejudicial actions, he could sacrifice the group's position for his own advantage, and the others would bear the loss. The article prevents that by making the mutual, representative character of the relationship a limit on individual action. You represent your co-creditors when you act on the credit, and a representative may not use that role against the very people he represents.
What counts as prejudicial
An act is prejudicial when it worsens the other creditors' position or diminishes what they can ultimately obtain. Condoning or remitting the debt to the debtor's benefit, compromising it for less than its worth, or otherwise dealing with the claim in a way that favours you at the group's expense are the kinds of acts the article guards against. The point is not that you can never deal with the credit, but that you cannot do so on terms that offload harm onto your fellow creditors. Where an act helps the group, it is allowed; where it helps you by hurting them, it is not.
The effect on your co-creditors
This provision does not necessarily make every prejudicial act void as against the world, but between you and your co-creditors it will not bind them. A creditor who acts to the others' prejudice remains answerable to them — he cannot escape sharing what is due and can be made to account for the harm his action caused. So even if you managed to take some step benefiting only yourself, the law does not let you keep the advantage at their cost. The safe and lawful course is to confine your solo actions to those that serve, or at least do not damage, the common interest.