In a very general sense a lot of reaction that are written in one step can also be written in two. I.e. alpha capture on carbon-131 is often written
$$\alpha + ^{13}\!\mathrm{C} \to ^{16}\!\mathrm{O} + \text{various photons and leptons} \,,$$
but may be written as one of
$$\begin{align}
\alpha + ^{13}\!\mathrm{C} &\to ^{16}\!\mathrm{O} \\
\alpha + ^{13}\!\mathrm{C} &\to ^{16}\!\mathrm{O}^* \to ^{16}\!\mathrm{O} + e^+ + e^-\\
\alpha + ^{13}\!\mathrm{C} &\to ^{16}\!\mathrm{O}^{**} \to ^{16}\!\mathrm{O} + \gamma\,(\text{6.05 MeV}) \\
\dots
\end{align}$$
However, in order for that to be reasonable, there must be a bound intermediate state to talk about.
In the case of PP fusion there is no bound $^2\mathrm{He}$ state (much less a bound excited state).2 Fusion only results if there is a weak tranformation at a time when both protons are very close to one another.
Nor can we talk about one proton turning into a neutron and then finding the other proton, because that intermediate state is energetically forbidden.
So, long story short, I don't think that you should write the proton-proton fusion process with an intermediate state. It's all or nothing.
1 A reaction selected entirely because I know it well.
2 Contrast this with the oxygen system where the excited states are real and have been studied in detail by neutron knock-out reaction on Oxygen-17.