In the remaining verses I feel Shantideva is saying essentially just one thing, and that is, practice.  We need to actually do this meditation to get a feel for it, otherwise it isjust an interesting intellectual exercise.  We should practice in meditation as has been described, and practice out of meditation too, until we complete this exchange of self with others. Just keep practicing.

Countless times in samsaric rebirths,
This self-cherishing attitude has caused me harm.

(8.155) O mind, because you wish to benefit yourself,
All the hard work you have done
For countless aeons in samsara
Has resulted only in suffering.

(8.156) Therefore, I will definitely engage
In working for the benefit of others;
And because Buddha’s teachings are non-deceptive,
I shall experience excellent results in the future.

(8.157) If in the past I had practised
Exchanging myself with others,
I would not now be in this situation –
Devoid of the excellent happiness and bliss of Buddhahood.

(8.158) Just as I am familiar with developing the thought “I”, “I”,
When perceiving my body, which arose from others’ sperm and blood,
So should I become familiar with developing the thought “I”, “I”,
When perceiving others’ bodies.

It is simple, really.  We just need to keep thinking I, I, with respect to others’ bodies and minds.  That is it.  Just keep thinking “me” when observing others’ bodies.  In order to bring about some deeper experience of this practice, simply think I, I, with respect to others.  “I” is just a thought.  Other than the thought, there is no I. We will see later on, in the next chapter, other than the thought “I” there is no I.   We think the I is one with our body and mind, which is why when somebody points at our body we feel they are pointing at us.  But we also think that our I is somehow separate from our body and mind, because we say, ‘my body’ and ‘my mind’ as if there was some independent part-possessor.  If our I were inherently existent, this is completely impossible, but this is exactly what we think.  In reality, our I is not one with its basis, nor is it entirely separate from it.  It is just the opposite of what we think.  When we see this, then there is no problem imputing our I onto the basis of others.  Until we realize this, we will feel anchored and fixed to this body, and we will remain self-centered.

We believe that others’, the self of others, exists within their body, too, don’t we? We conceive an inherently existent other within their bodies.  We naturally conceive an inherently existent other within the bodies of others.  They are inherently others, so they cannot be me!   This is also a mistaken belief.  There is no other there. There is no other there within their body.  Other, like I, is just mere imputation.  So we can impute “I” on others and “others” on ourself.

Once we realize it is possible, afterwards, it is just an issue of training and familiarity.  All we need to do is become more and more familiar with imputing “I” upon this different basis, the body or bodies of others. Thinking I whenever we observe or perceive others’ bodies.  Just keep doing it. Think “I” when perceiving others — so we can do that at all times, when we are with others and when we are just thinking about them, just keep thinking I, I, I.  Eventually, they become a basis of imputation, and this body eventually will cease to be for us the basis of imputing I, it will become the basis of imputing other.

It is clear if we cannot exchange self with others in this way, we won’t achieve much success in the Tantric practice of generation stage.   In generation stage we try to become familiar with the thought “I” when perceiving the body of the deity, the body of Vajrayogini for example.  Right now, the body of Vajrayogini is not our body, it seems to us to be a different body.  We feel it is someone else’s body.  But we know through training in generation stage, Vajrayogini’s body gradually comes to feel to be our body.    Our training in exchanging self with others is an excellent preparation for our ability to engage in our tantric practice.  In fact, it is part of our self-generation practice, because when we self-generate as the deity, we generate ourselves as all living beings in the aspect of Vajrayogini.

(8.159) Examining myself thoroughly
To make sure I am working for others,
I will take whatever I possess
And use it to benefit them.

Venerable Tharchin explains for as long as we impute ‘mine’ on any object within our possession, we continuously burn up our merit.  If instead we impute, ‘belongs to others’ on the objects within our possession, and we view ourself as the guardian of these things until we hand them over to others, then we do not burn our merit.  If we use these things for the sake of others, then we accumulate merit by having them.  In this light, it doesn’t matter what we have, it matters entirely what our imputation is.  This is equally true of ourself, our human body and mind, our time, everything.

If we have exchanged self with others, this practice becomes automatic.  If when regarding ourself, we think “others,” then naturally everything we own or possesses belongs to “others.”  With one simple switch of imputation, we are able to automatically give away everything we have to others without changing a thing.  Likewise, if we impute I onto others, then everything they have is felt by us to be “ours,” so there is no basis for jealousy or attachment to arise.  We already have everything.  Like magic, this one practice inverts all of our delusions into virtues.